Comment 6 for bug 96676

This looks to be a problem with vte changing to match XTerm's behaviour, and possibly XTerm not matching how terminfo thinks it behaves. shows the change.

It looks like the distinction is there to differentiate F13-F16 from Shift-F1 through Shift-F4. I don't understand the code well enough to see why it only applies to F1-F4 and not F5-F12.