I had the N91 firmware blues. I was having the theme reset problem and various other weird problems (including a beta version of ShoZu crashing randomly) reported by others as a problem with the V1.00.028.13 29.03.06 RM-43 version of the N91 firmware that I have (apparently V1.10.030 05-05-06 RM-43 and newer versions fix these problems as reported at mobile 9) until I reformatted the hard disk.

Fingers crossed, things are working now (for me a phone isn't working until ShoZu works :-) ! ). It looks like my problems were due to one or more of the following

  1. the firmware version
  2. the Nokia podcasting app (which is in beta)
  3. the Nokia Wireless Keyboard app (which doesn't officially support the N91 but I was assured would work)
  4. puTTY series 60 v3 beta or
  5. the ShoZu beta

which were the only apps I had installed (and yes I am well aware as an ex developer of the perils of running beta software which is why I am not flaming or blaming anybody :-) ! ).