sysui CustomTarget_solaris.mk not working

During install create phase, the sysui CustomaTarget_solaris.mk rule to create the desktop 
integration tar.gz
is never invoked:
$(solaris_WORKDIR)/%-desktop-integration.tar.gz: ..................
So build fails when trying to cp this file later.
I tried to debug the problem but I still cannot figure out why that rule is never invoked.
Also, I cannot understand why the Module_sysui.mk always runs slackware even when not building for 
slackware:
$(eval $(call gb_Module_add_targets,sysui,\
CustomTarget_share \
CustomTarget_slackware \
Package_share \
Package_desktop \
$(if $(filter rpm,$(PKGFORMAT)),CustomTarget_rpm) \
$(if $(filter deb,$(PKGFORMAT)),CustomTarget_deb) \
$(if $(filter SOLARIS,$(OS)),CustomTarget_solaris) \
))
other targets are considered, while slackware is always built.
thanks for any help!
Gabriele.