Got some good news and bad news.
Bad news - issue is still around and I don't think I'm going to be able to fix it.
Good News though - I have done a good couple hours of fiddling in SQL Profiler and Query Analyser and have found what I believe to be the issue!
Fault is not in the SQL stored procedure (which would have been convenient - that way I could have at least tidied it up on my side) but instead with the code calling the procedure.
Here's the SQL that is run (as per Profiler) when I save content to a page called "tessta":
exec dbo.Wiki_TopicAdd @moduleID=433,@content=N'<p>dfgdsafg</p>',@cache=N'<p>dfgdsafg</p>',@name=N'WikiHomePage',@title=NULL,@description=NULL,@keywords=NULL,@updateDate='2008-01-23 11:56:12:057',@updatedBy=N'Pieter',@updatedByUserID=39,@AllowDiscussions=0,@AllowRatings=0,@RatingOneCount=0,@RatingTwoCount=0,@RatingThreeCount=0,@RatingFourCount=0,@RatingFiveCount=0,@RatingSixCount=0,@RatingSevenCount=0,@RatingEightCount=0,@RatingNineCount=0,@RatingTenCount=0
The important bit there is the " @name=N'WikiHomePage' " - it shouldn't be saved there - it should be saved under the page name that is currently open.
If i run the same chunk of SQL (in Query Analyser) with the correct name (" @name=N'tessta' " ) it works 100% and can be viewed on DNN without issue.
This should then mean that the code that calls (and fills in the variables for) dbo.Wiki_TopicAdd is pulling the name from the wrong place. As to why I'm getting this and no-one else is i'm honestly not sure - but perhaps with this info someone could see if they could figure it out?
Please get back to me on this - thanks!