I've been noticing the same issue lately, using my iPhone with iOS 5.1.1
Haven't tried my iPod classic, I'll see if it does the same and report back. Anyone else have this issue?
335i E93 Le Mans Blue/BMW Performance Shifter
328i E92 Space Gray/BMW Performance Shifter/M-tech Lip/LED Halos
325Ci E46 Titanium Silver