My DH and my mum can be somewhat the same. DH and I have been together for almost 13 years and still there can be tension in the air (didn't help that they had a massive blowout not long after DS1 was born...to the point it took about a year for my mum to visit while DH was around). I too have learnt not to vent too much to my mum about DH, not that I did much anyway- kinda learnt that from the start as we (he was a friend of my brothers) had known DH and his sometimes silly behaviour before we started going out. Try and only point out the more positive sides to your DP and hopefully in time your mum can see the good that you see too.