I moved my site dzwiek.org from shared hosting to VPS and it has been great apart from search engine glitch:
The first time I search for something, there are 0 results.
Then, I search for the same string again and the results come up with no problems.
I suspect there might be some timeout variable to set in either php.ini or my.cnf
This is incredibly silly but I suspect this was caused by "search this forum only" being ticked by default. Basically users (and I) were trying to perform a search inside a forum where there was nothing to return from search query. Repeating the search straight away performed it over whole site returning search results...