A bug was reported that caused tabs to be formatted incorrectly when you edited tabs in the advanced editor, then switched to the standard editor.  Specifically, this was with fret numbers great than 9 (double digit notes).  If you have tabs that include a visible "_" , you can fix this issue by opening your tabs for editing, and then resave them,  The formatting will be fixed automagically.

Thanks for reporting issues, if you find something, contact me and I will address it!