Map Editor: fill command buggy

I made this feedback/suggestion post for the map editor.  I hope you can take a moment to give it a read.

 https://steamcommunity.com/app/230190/discussions/0/1694920442948483437/

However I wanted to create a bug report for a bug related to the fill command.  The bug is described in the above post, but I'll provide some crude pictures to help illustrate the point.

Bug: When using the fill command (ie. holding ctrl), sometimes the fill will "leak" diagonally.  See pictures below.  I will have to test to see if there is a specific way to replicate this because since it has happened, I've been trying to avoid the issue altogether by only filling in areas that don't have diagonal connections.

Solution (ideal, and how it seems to work, except when it doesn't): diagonal connections "block" fills.

Note: This bug is very frustrating since the "leak" could cause the entire map/layout/whatever to be filled.  Is there an undo command?  If not, have you considered adding one?  I think it would be very useful! :)