Pyinstaller QT5: upx compression windows error on program startup?

Question

Python

pyqt5, python 3.6, pyinstaller 3.1 or 3.4 dev, win 7 x86
doesn't work with upx compression,
Compiling: pyinsstaller progname.pyw
build successful
run:

cd .\dist\progname
progname.exe

And I get:

Program 'progname.exe' has stopped working Windows is looking for a fix for this error...
Program 'progname.exe' is not working A problem has caused the program to stop working.
Windows will close the program and, if there is a known workaround for the problem,
will notify you.
Debugging Close program

cd ..\..\
notepad progname.spec

I change the parameter to Build again and run:upx=Trueupx=False

pyinsstaller progname.spec
cd .\dist\progname
progname.exe

Successfully! The program is working.
Why doesn't it work with upx enabled? Maybe one, for example, a specific Windows library, does not need to be compressed?