daniel - none of the fixes below or otherwise worked in the long term and i was using b57. today i experienced the same problem in the usual sudden way so i thought the upgrade to b58 may fix it.
i am happy to report that, on update, the problem seems to have been repaired although i cannot be sure if this has been explicitly addressed within the software or if it was due to the upgrade cleaning out the existing catalogs and caches. i will report here if there are any further incidents re. the same issue. good luck.
