In case the UBB guys are interested, here's what the hosting company support guy said about flushing hosts:
"This usually happens when you have more connections to the MySQL then the default limit of 250 connections or you have a script that is opening connections but not closing them. I strongly recommend to review your websites code and check if all the mysql connections are being closed after they have done their job."
250 connections seems like not very many, doesn't it?
