So I have 2 models, with 2 different Armatures. One model is in one layer, second model - in another.
I created animations for each Armature using Actions Editor. Different naming and all. And then I noticed that each of the Armatures contains Actions from another. WTF?!?!?!?! Is it by design or am I doing something wrong or is it a bug?
Each Armature needs to have only Actions made for it. There is absolutely no need to jam everything together 
Please advise. Thanks.
Are they using the same armature data block, have you made them single users. Please supply example
I recorded video showing what’s up. Regardless if they use same datablock or not, the outcome is the same
I can’t wait when Blender loses that idiotic datablock concept (if that’s the case).
Blend file: http://www.pasteall.org/blend/34262
You can assign any action to any object. This is useful since you can create one person with a walk cycle, then select that walk cycle for another armature. That’s a feature, not a bug, surely?
Why would I want Actions from two entirely different Armatures merged ? That could be a feature when it’s done by designer’s choice, not automatically.
Imagine you have a tank and a character in the same scene. Why would I want to have more mess in as it is unmanageable list of Actions for either of the Armatures? Character might have 20 Action and tank might have only 4. I’d understand if there was some sorting / filtering implemented. Otherwise it’s just horrible mess when bunch of different Actions are jammed together.
Or imagine having 5 characters, 50 anims each (characters having different rigs) and each having Actions with the same name for the sake of clarify. You end up with idle, idle.001, idle.002 and so on. That’s just plain bad design.