While upgrading WP I deactivated the AskApache plugin and on reactivating I noticed that suddenly the tests fail. I didn't change any settings (I usually make a few folder writable before upgrading and then change them back and this time I did nothing else), but the htaccess tests (and mod_rewrite?) and something with fsock, no idea what it is. Since I have problems with newer versions I still had 4.3.2 going, but right now I can't get any version working after the test part was built in, so now I've got 3.5.1 which does the job.
I hope this explains the situation a bit...?
Could it be that my host had changed something or did I do something stupid without realising?