Don’t have alembic import/export 
Another stupid thing in Blender: Having to click on the option ‘Use Nodes’ in the node editor to start using nodes, if you are in that window you obviously want to use nodes, is like duplicated function. The worst thing comes when you uncheck the ‘Use Nodes’ option which does… NOTHING! LOL.
Inconsistencies everywhere in the UI. Scroll yourself to death issues. If the loaded file has changed on the HDD, no warning that it happened or update to the new one, you have to load each file manually again.
not having undo or lock for the 3d cursor.
Alt+G also resets deltas
file>external data > report missing files/find missing files (not apply to linked objects or groups)
#1 you need to render 3 passes to get a shadow under your object in cycles. .)
#2 in gme only global disable mipmaping available
#3 bermuda triangle for texture dynamic in game engine. only 8bit survive
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Attempting to change the canvas size of a generated image will irrevocably destroy changes made to it without warning.
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Any changes to any of the settings in the “Image” drop-down menu in the texture panel for Blender internal materials will, without warning, irrevocably revert any changes that have been made the corresponding loaded or generated image.
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The undo/history state system in general
The most absurd thing is that using multiple Blender windows under Windows is not working properly even in the year 2015 
Not sure why you say that, works fine for me.
Another one that annoys me is that there is no material/texture/etc. library. You can append from another scene, but it’s just ridiculous. For effective use you need a specific scene with materials stored in it which in practice is the material library, only it’s harder to use.
Texture paint directly onto your 3D-model for hours, use shortcut Ctrl+S to save your project, exit program… The lack of any warning whatsoever that you SHOULD have saved the texture seperately is the absurdest absurdity I’ve encountered so far.
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System/Program configs override user configs: http://blender.stackexchange.com/questions/19534/shared-network-install-config-priority …I mean WTF???
Gets me started everytime I think about it! -
Current Alembic development is not designed to be compatible with other Software Im-/ Exporters right from the start.
Quote from Lukas: “it’s just an internal caching feature atm. We are aiming to have some basic import/export from other software eventually and make the format more compatible.”
Maybe even worse… -
No ‘proper’ UNC path support. Everytime I load a windows scene with UNC paths on Linux, it gets messed up because the double slashes make Blender think it’s relative paths.
Annoying
Hold Alt?
Scattered display/shading options: shading mode in 3D view header, Display and Shading panels in the properties region, no global object display settings (wireframe, axes, names, etc.).
10,000 buttons every where, but when you do something like texture paint, somewhere in the midst of all of them is one that makes it so it doesn’t work… wait it’s not a button you don’t have the right node in cydes selected… wait no … (my 2 cents… obviously we all love blender…)
… ouch
- IO in general needs to be as SOLID as possible for serious adaptation in studios that rely on multiple softwares.
Currently you cannot import dominant architecture formats; Export to gameengines is weak (FBX and UE? ) and more importantly lack of Alembic (an OPEN FORMAT that is in EVERY other 3d software) is absent. That is a serious deal breaker as animations/fx/data cannot be efficiently shared beyond basic modeling(obj).
Texture preview is ~10 times slower when cycles is selected (compared to blender internal GLSL viewport).
- Use nodes button.
- As NRK said: 10000 buttons, with the ones for any given workflow are scattered all over the place. And where clicking on one can stop anything working in the scene.
- Material system. No “material editor”, nodes in a node editor, mixed with the weird linear depiction of the node system in the properties window. Nodes too basic, no ubershader. No material library.
- Coordinates shown in Porperties panel. They are neither global, nor local (of a parent object) coordinates. They seem to be local coordinates of the parent object, minus the difference in coordinates of the two objects at the timepoint that the parent relationship was created. Or something… ok, someone please explain!
List view is a small Outliner inside the property window. It is a scrolling window inside a scrolling window, it’s a tiny window for possibly many properties. It has same functionality as Outliner.
material system? cmon… blender has one of the best material systems. I just don’t understand why does everybody whim so much about ubershader. I can build any material MR-s mia_material can do in not more than 3-4 steps and it will be much more functional and faster than mia material. Using blender’s node editor for building materials is a pure pleasure, fast stable and interactive, again: interactive and incredibly fast, and stable. i can say for sure, maya users can’t even dream about such interactivity.
As for absurdities - inability to deselect everything when clicking on an empty area. (i may be wrong, and it could be really simple to setup, but i’m aware of “a+a” and its not what i mean)
Not being able to see the total tris of selected faces