Seems a bit tough to assume attitude issues. If he was on loan to MK Dons and they've now bought him permanently, that suggests no problem there.
Maybe he's just not good enough?
All I'll say in regards to potential attitude issues was, there was that apparent phone incident not long after Lambo took over. Conjecture of course, and possibly just a bit of foolishness on Samirs part. It may well have marked his card somewhat with Lambert, even despite it being a fairly innocuous incident.
Last pre-season in a couple of games he did, to me anyway, seem to have a touch of the Bellamy about him. Very prickly sort of player. Liked to square up at the first sign of a firm tackle coming his way, and spent a lot of pitch time moaning at the ref. At the same time though, he couldn't seem to channel that firey attitude in the way Bellend could at his best, and obviously aside, lacks the pace that Bellend could call upon.
He looked a bright spark in those cameos in McLeish's reign, but then again, it came at the end of a very long, hard, dreary season. May just be a case of not being rated. I also remember him being far more lithe when he first broke in and having a bit of acceleration on him. He looks bulkier now, and alongside the injuries he may have lost a couple of yards of pace and not have the attributes to make up for that. His first game this pre-season he looked good in the opening stages but seemed to fade out the game a bit.
Good luck to him though. I'm sure if there are any hints of a billy big bollocks attitude, that a permanent move to MK will ground him, and he'll have to work bloody hard to climb the leagues again.