Undo Button Faulty/absent

This deseperately needs more attention. We are new users and TWICE within 10 minutes accidentally replaced a pretty large conditional loop block with an empty block simply by dragging in a wrong spot without any means to undo this mistake. It’s not even our mistake per se, but serious drawback of the HS’ interface (why on earth a block would replace another block upon dragging??) and not being able to undo it makes it even more terrible. This issue should be given absolute priority to fix, as it’s a huge source of frustration for new coders.