partCombine confused by tags

[David Sumbler]

I have just spent half a day trying to work out why one staff in my
orchestral score extends beyond the final barline.

Eventually I found out that it is because \partCombine seems only
partially to understand tags.

The following example illustrates this:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\version "2.21.2"

instA = {
  b'4
  \tag #'versionI c''
  \tag #'versionII d''
  b'2 }
instB = {
  g'4 g' g'2 }

\score {
  \keepWithTag #'(versionI)
  \partCombine \instA \instB
}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

PartCombine chooses the notes for the instA line in accordance with the
tags, but adds a crotchet's worth of staff after the end of the
passage.

It also does not correctly combine the parts after the tagged section. 
However, this can be got around by adding a \partCombineChords
instruction before the 3rd beat of the bar.

Does anyone know of a way of correcting the extended staff?

David