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

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.