My understanding is that putting the time signature between the two repeat brackets is standard and would not be affected by directions about key signatures or accidentals.

EDIT: My apologies: i see what you mean about the closing line of the repeat bracket; I thought you were talking about something else.

Yes, this seems to be a strange bug.

You could insert an extra measure before measure 3 and set its width to zero (and exclude it from Measure Numbering).

If playback matters, you have to set it to something like an invisible 1/64 Time Signature.

see: www.hochweber.ch/repeat.mus

Jurg, you have indeed shown how any user attempts to remedy this is only a partial solution with inherent compromises, which strongly suggests that Finale developers should address this rather than relying on user work-arounds.