For me (on my config, not the one added in this thread, it's just "X Lines"
So if I select a single line ("1 Lines" is shown). If I hit tab, the cursor is moved from col 0 to col 4 (where the actual text starts), but the overall effect on the line is nil (only the cursor position moved). If I select multiple lines, for the last line in the selection, the cursor jumps to col 12 (which is where the text/code starts on that line).
This behavior seems consistent with simply putting the cursor in the blank indented area (before a text/code line starts) and hitting tab. The cursor jumps to the beginning of the text/code line (skipping all the blank indented area).
It seems like the selection is simply being ignored. Keep in mind that shift-tab does un-indent though.
If I get a chance today, I'll try it with a fresh/blank config.
Jeff