"[...] so don't worry about losing any pieces."
You can actually lose a piece when there is a purple trigger:
1) You move a piece on the trigger to make the purple blocks be disabled
2) You put a piece behind one of the disabled purple block.
3) Then remove your piece on the trigger to re-enable the purple blocks.
Even if you re-enable the trigger, the piece is now forever gone!
This can be reproduced on Level 21.
That was probably not "intended"? But we can reset the level when that happen. ;-)