[IanD]

Interesting. Obviously I'm not sat here hitting the F5 key

Just tried it in IE (was using Firefox before) and guess what, you were correct, no duplicate mysql query. Get the same log lines at 30 seconds (retry with new instance etc) but the php script is not reloaded. IE has a 408 Request Time-out page, not something I've seen before but this all sounds like this is the correct behavior. Perfect.

Just need to need to work out the difference with Firefox then - I've never come across something like this before.

Would Firefox automatically refresh the URL if it's sent a 408 Request time out header? That's what seems to be happening. If it is it does it very quietly because FireBug doesn't pick it up.

Now looking carefully for a split second I can see in the status bar of Firefox at 30 seconds making a new request. Also tried with all add-ons and plug-ins disabled.