It happens every time. i restart radiant, my computer and nothing changes. It happens on all of my computers. even the best 1 in the house(mine ) getsthe same problem in radiant.
The problem seems to be not in the computers but in how you are trying to bend the patch mesh. The only way you can do that is by selecting the patch, pressing V on keyboard, selecting a pink dont and then moving it up, down, right, left, forward, back.
in other words .try moving the all the vertices where u want them to be .its pretty futile and hard way specially with big meshes (alot of faces).y shouldnt u use the bend mode?it works for me fine and i havent seen any problems with it.there are 2 guesses i can make right now
1\the .map file is corrupt and has an error somewhere so bending the patch would make the error surface .
2\ur bending the patch in a very wrong way ,seems like ur trying to create an uncreatable patch .in other words u bent it 2 much.
u could try bending the patch outside the ur map ,like in an empty map with just the patch u want 2 bend.and if it works make it a prefab and loaded in ur map .make sense?