Trim Trailing Spaces is known for breaking undo: it was reported here: http://pspad.nlift.com/issues/143/trimspaces1-breaks-undo/ . I hope it will be fixed soon.
On-demand (on-save) trim was also proposed several times and seems witty, but I am not sure it got any positive response from mister Fiala yet. -- <http://forum.pspad.com/read.php?6,55295,55572> PSPad freeware editor http://www.pspad.com
