I just discovered something interesting....
So I used ShellMenu to revert my Windows 10 interface to a Windows Classic interface. And what ho, my Poser Pro 11 Library buttons all change to Poser Pro ( yes, that one before Poser Pro 2012).
Looks like Poser used fall-back icons instead of generating icons from SVG files.
I've encountered this few times, but for me it always disappeared after Poser restart or system restart.