Same here. That is really strange.
I believe I got the point here, you want that faces on the corner to stay straight connecter to each other where you have a corner. Is that right?
In that case, you cannot have a seam marked there.
Seams are used to make a cut on your mesh, if that cut is not straight, there is no way it will be straight unless you don’t make that cut.
Sadly you will end up with something like this:
If this was my project I would make the map with the cuts and fix any problem on the corner using the texture paint mode, if necessary. But you know, corners are places where cuts are really easy to fix. They are supposed to be folded, so any imperfection is not so complicated to fix as in the middle of a flat surface.
Yes, that result I cannot understand, because it does not happen here.
Could you provide a blend file with that part of the mesh?
1.blend (488.2 KB)
Here is the reason of your headache:
If you look from the front view you see that the faces are not well aligned.
Do you see on the corners?
No way. Damn it.
yes I understand. I’m so ashamed) Such a trifle. How could I not have noticed) OMG)
And look at this corner seam:
It does not make a 45º line, so I suppose you are going to have problems there too.
nah, everything is correct her)
Ok, I just guessed that the sides were supposed to have the same depth as the front side. If they are supposed to be larger, its ok, then.
Lol! It’s perfectly fine. We all do some basic mistakes sometimes. I am a master on doing that and taking ages to figure it out.
Just remember, the top, left, right, and so on isometric views are your most powerful tools to diagnose those things. If something is not working as it was supposed to, inspect your model from all the angles.