Auto-join of `Border` is not always working

[tig]

Run Frames Demo:

I saw this a long time ago, but all of the discussions of "finishing" Adornments (#2994) reminded me it's broken.

[BDisp]

I saw this a long time ago, but all of the discussions of "finishing" Adornments (#2994) reminded me it's broken.

Yes, that was after the new title drawing.