I have find a bug in Geany 1.22 : if a Txt2Tags file which contains 20 "-" on a line (--------------------) after the header, Geany crashes. I think the bug is due to an error in coloration rules.
OK, I tried 1.22 and it didn't crash, but it entered an infinite loop, which is just as buggy.
There is a bug with signed vs. unsigned comparisons in HasPrevLineContent(), but for some reason it doesn't lead to a crash or a loop with the latest version, one of the calls must have been fixed to properly handle invalid positions. I'll try to fix it properly but the effects of the bug doesn't exist in development version.