I'm trying to set up a simple subdirs project with 1 application and 1 dll (on windows)

My application has this in the .pro file: (simplified it)
dll.path = $$OUT_PWD/debug
dll.files += $$OUT_PWD/../lib/debug/lib.dll
INSTALLS += dll

the dll project is called 'lib'.

When running qmake after a clean, the makefile does NOT have 'make install' rules for copying the file.
Only when I build the library, and the .DLL actually exists, will a second invoke of qmake update the makefile with a 'make install' rule that does the copying.

Am I missing something? Is this a bug?

I've tried doing it the other way around, letting the library install itself to the application build dir, but the problem remains. The .dll must exist for qmake to accept it as an install rule... (???)