qmake asserts !isEmpty when using DESTDIR=

C:\kdab\qmakestaticbug>qmake -recursive
Project MESSAGE: Install prefix is "C:\KDSoap-1.0"
Project MESSAGE: This is KD Soap version 1.0
1 file(s) copied.
Reading C:/kdab/qmakestaticbug/unittests/unittests.pro
Reading C:/kdab/qmakestaticbug/unittests/webcalls/webcalls.pro
ASSERT: "!isEmpty()" in file c:\iwmake\build_vs2005_commercial_________________p
adding_________________\include\qtcore\../../src/corelib/tools/qlist.h, line 263

This is fixed by using DESTDIR=. instead of DESTDIR=, as suggested by Ossi, but here's a bug report so that the assert is replaced with a better error message.

Note that the .confqmake.cache (which becomes .qmake.cache when parsing the toplevel .pro file) matters.