Sorry; I kept getting a page come up after submitting the post that said that the page had been removed or something along those lines so I didn't think my post had been submitted. I noticed after posting today when I was checking the other post's that I had been successful before.
Apologies once again - I wasn't attention seeking!
Mine has always done this occasionally, typically when the hood has been folded for some time (e.g. after taking the hard top off). I guess if the fabric is a little tight the downward-pointing tabs don't quite get grabbed by the rollers that (I assume) pull the rear of the hood down & tight. As you say, it works after momentarily releasing the button ... it's a very minor inconvenience (and has never got any worse), so I've never bothered to investigate.
If yours does it consistently perhaps the hood needs adjusting. Has it had any work done (e.g. new hood or plastic windows replaced)?