IPhone :: First Few Seconds Of Sound Missing With Bluetooth?

I've been struggling with this issue for some time now, and haven't found any explanation. The issue is that if I am using turn-by-turn navigation software (that speaks directions) while my iPhone 4 is connected to a Bluetooth device, and the software hasn't given me directions for a minute or so, the connection seems to "go to sleep." When the next directions are issued, I miss the first part. For example, if the directions should have said "Get ready to turn left at Main Street," all I might hear is "at Main Street." Quite unhelpful!

Some details: I have tried two different navigation programs. I used MapQuest's free app for a while, and now am using the VZ Navigator app. Both had the same issue. I have also tried three different Bluetooth devices: a Plantronics Voyager headset, a Jabra headset and my car's Bluetooth speakerphone. All show the same behavior. Also, if I'm playing music through Bluetooth in my car, the problem goes away completely.

My conclusion is that the iPhone 4 is letting the connection with the Bluetooth device lapse when not in active use for some length of time, and it takes a few seconds to re-establish it. But that doesn't lead me to a solution. Anyone else experience this, and know of a fix for the problem? Is there any way to keep the connection alive without playing music, which I would obviously prefer not to do with a headset!