It appears that the latest firmware update pushed out of Sony Ericsson for the Xperia X10 smartphone seems to have some kind of WiFi bug, which apparently lets WiFi turn itself off.
According to an article over on Enagdget Mobile by Chris Ziegler, by way of Se-nse, what happens with the Sony Ericsson Xperia X10 with the latest firmware version is that any time the mobile signal drops to nothing then bounces back, WiFi switches itself off.
It seems a fairly brutal bug as most probably the reason you are using WiFi in the first place is probably because you are getting a weak signal.
Other than that there isn’t a lot of detail on which Sony Ericsson X10’s are affected; however apparently word is the offending version is R2BA026, so the suggestion is users keep away from that until such times as Sony Ericsson pushed out an update. We do have a very short video of this bug in action though which can be viewed below.