cmake plugin swallows additional arguments containing = characters

The cmake plugin swallows additional cmake arguments given with a -D option if the value of the argument contains a = character. For instance this works perfectly:
-DRSC_DIR=${WORKSPACE}/RSC/labelfoo
but:
-DRSC_DIR=${WORKSPACE}/RSC/label=foo
is not passed to the called cmake. On a normal command line in linux this is not a problem for cmake. I've also tried to quote the path with no success.