[NamTaf]

My Diamond Rio PMP300 would play VBR but would shit the bed on displaying duration and seeking because it assumed CBR, as you suggested. When VBR was new, this was a pretty familiar situation and oldschool mp3 encoding standards for share sites would give the option to stick to CBR for that reason - they'd specify alt preset standard for VBR and a couple of CBR options, generally around 256kbps.