Some time ago (not sure when) indent behavior was changed when you had highlighted parts of a line. Before it would replace the highlighted text with an indent, now it will select the entire line and indent the line forwards or backwards depending on your key presses.
Shown in the video below is the studio editor (top) with the bug and a sublime text window (bottom) showing the old desired behavior.
- open any script in roblox studio
- type out any line of text to test with
- select a portion of the line and press tab, observe the behavior
I can repro this 100% of the time on a windows 10 computer running studio version 0.356.0.224916