Have you encountered such issues using Claude Code to modify B4X code? I find that it often struggles with editing the file because of the tab indentation.
I have made extensive use of Claude Code (pro) over the last 5 - 6 weeks on B4A/i/J projects of all sizes and with lots of tab indentation - with no issues like you suggest.
Can you share a small project with the problem and what prompts you were using?
As an aside when I click on your TextBox.bas link I get
Oops! We ran into some problems.