Help Wifi switching problems

[sefu]

This seem to started happening after I updated to 1.72.405.3.
Sometimes the phone wont switch to wifi to connect to my home or office network. If I go into wireless settings, it shows wireless as disconnected and if I hit scan it doesn't actually scan.

This only happens sometimes, I noticed it happens mostly when I have been connected constantly to 3g for a few hours.

This is also a problem with my regular desire, anyone know if there is a fix?

 

[sefu]

I forgot to mention, if I switch the wifi off then on, it will work again.