rendering differences if using `-j12 CPU_COUNT=12`

[Werner LEMBERG]

Folks,


since some weeks I encounter a very strange problem while compiling
git HEAD.  I get different rendering results for

  make doc

vs.

  make doc -j12 CPU_COUNT=12

as the attached `1-*.png` images show: in most cases, the glyph
`accidentals.sharp` in the `-j12` build is replaced with
`accidentals.sharp.slashslashlslash.stem` if rendered in markups.

However, there is also a file where apparently the `-j12` build is
correct, see `2-*.png`.  On the other hand, if I compile the affected
file manually (the first example in the NR section 'Music notation
inside markup'), everything's fine.

This happens reliably with my setup.  I didn't observe this earlier
since my old laptop didn't have 12 CPUs.  However, I can't say with
full confidence that it didn't happen.

Does anyone else see this, or maybe a similar problem?  Unfortunately,
I have no clue how to tackle the issue.  Any ideas?


    Werner