I put four 3rd party .so files in total in same folder. And qt can find 3 of them, except only one: libMPCtrl.so

Below is part of my pro file: (notice that I just put three .so files to LIBS but interestingly, qt find another one automatically.) How can I make qt find the libMPCtrl.so ?

unix{
LIBS += -L$$PWD/lib -lhcnetsdk \
-lPlayCtrl \
-lMPCtrl
}

INCLUDEPATH += $$PWD/include/ \
$$PWD/Configuration/Public/ \
$$PWD/lib/

(It doesn't matter whether I use . or $$PWD, same result.)

I mean, actually instead of "cannot find it", qt even didn't TRY to find it. According to strace tool, qt never tried to open() this .so file.