good morning,
it seems a little bit difficult to get it. i reproduce the bug...but i can´t figure out the trigger. it is no specific weapon or skill.
yesterday i tried to reproduce the bug. here we go: first everthing was okay. i start the game and go to shop. go on a item, push the upgrade button and everthing was showing correct. i also upgrade the weapon one time. unequip many items...equip...unequip...upgrade button...it was a some kind of stress test from me. ;) everthing was okay. ok then i played a level. after the level i go to the shop to take a look of the upgrade...mhh everthing okay...another level -- shop -- ok -- another level -- shop -- ok -- another level -- shop -- not ok!
http://dl.dropbox.com/u/37693147/P20120126190615.png
http://dl.dropbox.com/u/37693147/P20120126190656.png
http://dl.dropbox.com/u/37693147/P20120126190713.png
after a restart it looks again okay:
http://dl.dropbox.com/u/37693147/P20120126191005.png
http://dl.dropbox.com/u/37693147/P20120126191020.png
http://dl.dropbox.com/u/37693147/P20120126191032.png
the strange thing is, later the evening i played soulcraft again. only one level before i go to sleep...i also take a look on the upgrade button and it was incorrect.