i updated today to SVN rev 1578 and found, that it is not possible
to use more than one custom variable for a single expression any longer !
i have set-up my project templates with custum variables as follows:
WXVER = 26
WXREL = 1
WXVERREL = $(WXVER)$(WXREL)
WXDIR = d:\wx$(WXVERRREL)
WXDLL = wxmsw$(WXVER)
...
all my projects are broken now, because the WXVERREL macro expands to ""