I've tried full screen and windowed. My mouse is a Logitec MX 510, not really any updated drivers for it, more or less just a standard HID compliant mouse.
The series of events are, launch game, get into combat, cast spells, mouse icon is ok for awhile, then when switching around characters (1,2,3) select a spell again and the mouse icon for the spell (say M.minor missiles) disappears. I can move the mouse around and can select targets if I get the mouse over it (while invisible, can only tell by the icon on the target changing). If I close the game and relaunch the icon comes back for a little while.
Also have an annoying bug sometime with warrior getting stuck on knockdown. Have to switch characters (1,2 or 3) to get off him. But that's not the mouse icon issue.
Thank you for any help, love the game but this makes it very hard to play. Any way I can help/support please let me know.