Not sure yet if something wrong on my Foundation installation or a new SP2013 bug. On SP2013 (didn't happen on SP2010!) - create new Document Library app and use Advanced Settings to set it to Manage Content Types. Then add a new Content Type (I used Link to Doc but Image etc - all seems to be same). Note it is not yet "Visible on new button" (which should be the default once added) so click "change new button order and default content type" to set it - no matter what you do here, it's ignored!!
So basically you can't add any further CT, just have the standard Document CT. Further, it shows the additional CTs (without the Visible ticked) but of course they aren't on the New button!
Am I the only one with this serious problem?
NB: Just remembered I did successfully add links in one Doc Library on this SP2013 farm, but deleted it a while ago and now all new Libs have this behaviour. The only major thing I have done since then is install Office Web Apps on another server and connect it to the farm, which naturally should not have this impact, so may be not the culprit. Anyone with this showstopper please say!