Strange behaviour of including Qt static library

Question

I'm using Qt 5.15.2 mingw 64 bit.

I compile a very simple static library and then include it to another qt app.

The strange thing is while compiling the app qt call MOC for every included header from the library which has QObject derived class, and then compile moc_*.cpp file. Shouldn't qt already put compiled *.moc files to the library?

The problem is that it takes a lot of time for multiple files. But logically all needed stuff have to be inside the library, no need to run MOC for that files again.