I’ve removed the original search function from the theme I use (Anaconda). I noticed that if you attempted to search whilst on certain pages, the search function was not correctly parsed.
Having had a quick poke around the code and, not surprisingly, not being able to trace the fault, I’ve bodged it.
The original search box in the header has been removed, and a (working) similar box in the right hand column.
If anyone notices other errors, I’d be very grateful if they could either leave a comment, or contact me.