Just checked, and lierduh you also suffer from this bug... so I'll assume that everyone who has done this also suffers from it.
The change I've made isn't aesthetically pleasing, but it does work and stays true to the spider friendly purpose.
To summarise to those joining the end of this thread and wondering where to begin:
First, follow fastforward's instructions on the first page of this thread... you need to do this before anything else to be familiar with what is going on before it gets scarier:
https://vborg.vbsupport.ru/showthrea...threadid=18035
Then follow lierduh's instructions within his post... there are several major improvements over the initial code.
https://vborg.vbsupport.ru/showthrea...137#post348137
If you're confident at this point and everything is working, then go through the whole codebase and replacing the relevant forumdisplay and showthread parts with the new format... stripping out sessionhashes as you go along (I've disabled the option in user prefs to not use cookies and made cookies compulsory).
Finally... to resolve the nagging bug about sorting and page spanning, do the stuff in my post above:
https://vborg.vbsupport.ru/showthrea...256#post418256
It's a lot of work, and certainly daunting. Would I attempt it if I were seriously unsure about this stuff? Nope. But if you are comfortable working with the template system and editing the php files... then the benefits of being spidered are considerable and can do a lot for your forum (increase members or increase advert revenue).