Reaper 5.32/5.33pre5 32bit, Win7 64bit.
How to reproduce:
1. Add an item
2. Set time selection
3. Click on the item with Shift modifier(on Windows)
There will be no a new step in Undo history, but after Ctrl+Z time selection will come back to previous state.
Originally Posted by vitalker
Mouse modifiers don't depend on such a behaviour, so I consider it's a bug.