Ok, I've fixed the crashing bug that I've found as well as a few other bugs I noticed.
From the picture files I can see that those tiles actually have an 'invalid' black, as that it's not zero on the colour ramp, but colour 13 (of 0-15). All the other tiles seem fine apart from these. So if you draw with the 4 colour remapping on you'll notice the bottom two tiles are mapped to that 4 x black range.
If you turn on the 16 colour tile palette range it all works OK, however on the screenshot you've posted I can see from the palette marker that the cursor is over a black from the blue range. How that got there I'm not sure as it's not in the images you sent, maybe it's from the earlier blue line colour bug?
I can only guess that this blue range value messed up the tile recolouring, but as to quite how I'm not sure as I haven't been able to duplicate it yet!
Anyway, I've updated the test zip to fix those bugs I've found and I hope that stops the crashing. But the way it's going another few bugs will appear!