If I drag the material over the wall. I get the mapping/color size issue, if I try to undo after that, I get the undo error.
However, like you say, if - after dragging the new material over the wall, I then create a new object, move it, etc. , I can undo just fine.
With the exception that the material error is never "undone" but it does not give me an error dialog.
I have not tried rebooting my system after this started. I can see if that changes anything.....
Upon REBOOT i am no longer ale to reproduce the Undo Error
Edited by Bartjuan, 24 February 2016 - 04:38 PM.