The bug where signs create invalid wall tiles has not only to be fixed as all saves of version 70.1 (both beta and now) need to be fixed because invalid wall tiles made diamond slightly destructible(i have a save that demonstrates that glitch) and we can't flood-fill propperly because of these wall tiles now... just try bugging up your save with signs and flood-filling something: You can't do it without using normal brush to fill the blanks.