[xslt] xsltproc error during parallel docbook building

[C Y <smustudent1 yahoo com>]

Hi!  BRL-CAD is attempting to use xsltproc to build our docbook documentation, and we're getting an intermittent error when doing parallel building (e.g. firing off a lot of xsltproc commands at once):

xsltApplyStylesheet: saving to lessons/en/mged11_refining_mug.html may not be possible

it's not specific to that one file and appears to occur randomly when a lot of xsltproc instances are running.  Restarting the make process usually immediately succeeds. Is this a known limitation of xsltproc?

Thanks,
CY