When I copy code out of a MLC that is current throwing an error and the line that is highlighted red, the red color code is copied also, so I get a [color=#c02a2a] and [/color] in my copied code.

Ah, right, didn't think about that, and bit weird that factorio would copy its internal markup, but should probably fix it by cleaning the textbox text when it gets clicked and before focus activates.

0.0.29 should have the fix.

It has one side-effect of not placing cursor where you clock in that box if there was line highlighted there, but idk how to fix that.
Issue seem to be that when text is changed after click, factorio just puts cursor at the end of it.

Can be fixed on the user end by clicking twice (unless it scrolls the code, I guess), or should be possible to disable highlight if it gets too annoying.
Lua often points to a wrong line there anyway :)