With the M5 changes to the Common Navigator (are you sick about hearing about this yet?), the caching of the association between objects added by the content provider and the the navigator content extension has been temporarily removed. The reason for this is to make sure the behaviour of finding the correct navigator content extension for a given object is always the same (previously it was not, depending on the state of the cache).
As bug 262675 has revealed, it was possible to have an object in the cache associated with a navigator content extension, even though that object did not match an expression defined by that extension. This is because all objects provides by the content provider were blindly added to the cache. Since the cache has been removed, it has revealed cases where the navigator content extensions were not setup correctly to account for all of the possible objects (one of these was missing in the case of the above DTP bugs). This will require a simple change to fix (look at the patch associated with the bug report).
It is possible that this problem may show up with other users of the CNF. The problem has always been there, it was just very non-deterministic and hard to reproduce given the cache. Now these problems with show up quickly so they can be fixed. I will also be done some work for M5 (tomorrow) to make the error handling of these cases work well.