Hey, so I have found and fixed one problem with dependencies:

In Win32, include file names can have different case from actual files (e.g. Header.h and #include "header.h"). There is a caching mechanism for filetimes to speed things up that was not ready to cope with this.

Now fixed: https://github.com/ultimatepp/ultimatepp/commit/4315ff493bc2 94e2dc2707062be95b998376768f

Can this be the problem?