1- open "memory_eater.blend" find here https://www.dropbox.com/s/6d7qwawdmetog0u/memory_eater.blend
2- check you ram with system info or something
3- start to delete all shape keys one by one using "Remove shape key from de object" button
Result: the amount of ram grow and grow to infinty and beyond and blender frezzes
Checked this issue.
The thing why simple transform doesn't take so many memory is that there're DIFF-ing happens when writing chunk to undo buffer, so almost all shapekeys are not re-writting to memory. But when you're removing shapekeys it's changes their placement in memory and this takes much more space in memory.
This might be improved in some way, but wouldn't actually consider this is a bug. Added note to our todo list http://wiki.blender.org/index.php/Dev:2.5/Source/Development/Todo/UserInterface#Undo.2C_Redo_and_Operator_Context
Thanks for the report, but marking as TODO now.