I guess somehow the system used the previous plug-in even the version number shown was correct. I deleted the file, emptied the browser cache and reinstalled. Now the library server seems to work. Also, seeking is possible now. It seems that MP3, WMA, APE and MPC files can be seeked, but not OGG anymore. ...your next project, perhaps?
Though, the 32-bit mode has an issue with track changes to other formats (I tried OGG). After a track change a loud buzz comes out instead of the next track. This happens only on server connection.
Also, with or without the library server the 32-bit mode seems to produce a warbling artifact now. I tried Wave out, Direct Sound and ASIO. All three output options have this problem. Something must have changed somewhere because I couldn't hear any audio problems with the previous plug-in version.
I could test this more and on other PCs, but it would be nice to know first if you can reproduce this warbling.