A few people have reported this problem in D:OS EE, predominantly in OSX, and there was a fix for this in the OSX release of D:OS 2, though that didn't completely eliminate the problem.
Try resetting your mouse configuration, or lower its DPI if it is very sensitive. At least for D:OS EE in OSX, disabling mouse acceleration could help. There was also a 'Precise mouse tracking' workaround in the configuration settings of the OSX version that could help (as well as for other mouse issues).
see
Cursor/Inventory selection bug...maybe?Try switching to windowed or fake fullscreen display mode, and/or lower the game resolution, to see if that makes a difference (windowed and fake fullscreen have fixed this for a couple of people, at least).