Invalid timestamp for bmake

[Frederic Fauberteau <triaxx%NetBSD.org@localhost>]

I experienced a failure for fonts/unifont in the installation step when I ran a bulk build:
===> Installing for unifont-13.0.02
=> Generating pre-install file lists
set -e && /usr/pkg/bin/gmake -C src
gmake[1]: Entering directory '/var/pkgsrc/work/fonts/unifont/work/unifont-13.0.02/src'
install -m0755 -d ../bin
install -m0755 unibmp2hex unicoverage unidup unibdf2hex unibmpbump unifont1per unifontpic unigencircles unigenwidth unihex2bmp unihexgen unipagecount ../bin
install: unibmp2hex: stat: No such file or directory
gmake[1]: *** [Makefile:53: bin-stamp] Error 1
gmake[1]: Leaving directory '/var/pkgsrc/work/fonts/unifont/work/unifont-13.0.02/src'
gmake: *** [Makefile:77: bindir] Error 2
*** Error code 2

After inspecting the $WRKDIR/src/Makefile, the 'bin-stamp' target (that produces the output above) should not be processed since it is during the building step. I have the feeling that the file timestamping is incorrect. FMHI, it is related to PR pkg/54878. This error occurs only when I use pbulk and sandbox with a chrooted environment.

I wonder if the fact that WRKDIR is on a null file system could be a reason for this problem:
/dev/ccd0a on /mnt/ccd0 type ffs (local)
/mnt/ccd0/nbsd/sandbox/nbsd9-hydralisk/work on /mnt/ccd0/nbsd/sandbox/nbsd9-hydralisk/chroot/var/pkgsrc/work type null (local)