Thanks for playing :) I definitely want to make more levels - maybe will do that after some time.
Undo / redo are there to help solving the puzzle - in previous games I made this feature was lacking -- and I did want to include it this time.
About the error - no, should not be related to the hotfix. This is another problem (I thought I solved it, seems like I ran build on the wrong commit) -- L should open a file-select menu when it can find a way to do so via OS, and I accidentally shipped part of the gtk with the game without its dependencies (libglib depends on libpcre which is not shipped); a workaround for that would be installing gtk on your system and removing shared libraries libgio, libglib, libgmodule and libmozgtk from the bin/ folder. Or just removing those -- then the game will just leave a warning that no backend for file-select was found.