I have an iPhone 4 with FW 4.3.3. Lately when I switch the mute button it doesn't give me the vibration feedback as usual. But when I switch back in to ring mode it suddenly does. When the phone is in locked it does the exact opposite, it vibrates when I mute it and doesn't when I unmute it - that's how I want it. But the reaction is not consistent. Anyone else have this? BTW vibration alert is set to be on in both cases. I find it super annoying, since I want the vibration feedback only when I switch into silent mode like it did until recently. I'm just talking about the feedback here, the phone does what it should in the respective modes.
I'd check with a Genius at the Apple bar if available to you. My new out of the box iPhone 4 did this and they had to trade it out. Guy stated that they usually only see this after a couple of years of use, but there are always exceptions. edit - just noticed Austria - are there international Apples stores?
We don't have any Apple stores, the only thing I could do is go to the provider I bought the phone from. It's bothering me like hell, but is it serious enough to warrant an exchange? BTW the phone is jailbroken, could that have anything to do with it?
I have the same thing on my 3gs running 4.3.2, only difference is that vibration is completely random on mine. Sometimes it vibrates when switching the button, sometimes it doesn't.
There was an issue with the jailbreak on 4.3.2 which caused this bug, but updating to 4.3.3 and using the latest redsn0w jailbreak fixes the issue. But you say you are already on 4.3.3. A restore will almost certainily fix it. Set up as new and jailbreaking with the latest redsn0w should fix the issue