Going on Holiday as a Step Family

I became a custodial step-mum 6 years ago - my stepson is now 14 and lives with us full-time except for 4-6 weeks holiday each year visiting his mum/half-sister/half-brother. His mum speaks to him twice a week but other than that doesn't play a parenting role or contribute financially. My stepson is a really nice, kind and intelligent kid and we generally get on well with all the usual stuff of family life - homework/chores/values/friends etc. His dad and I discuss everything regarding his son/my stepson and I am involved in all the decisions - we both go to parents' evenings, we both watch him play rugby every week, choose his presents, help him with homework, discuss difficult issues etc so essentially a strong unit bringing him up together, but obviously with different relationships with him as you would expect with a bio dad and a step-mum.BUT when we go on holiday it all seems to fall apart. My stepson suddenly becomes very threatened by my presence and becomes exceptionally needy and clingy of his dad - it's as though he has regressed by about 5 years. He addresses all his conversation to his dad, does anything he can think of to get his attention, starts to pick on/criticise every single thing I do or say and constantly reminisces about stuff they did/things they had before we met. He gets suspicious that we are trying to do things without him - even if it's going to the cash-point for 5 mins while he is playing table tennis with a friend he's made on holiday. It's like having a completely different child. I do my best to ignore his behaviour and not react, but it's hard to enjoy a holiday when you feel ignored, criticised and under the microscope the whole time. We got back from holiday yesterday and my husband acknowledges his son's change in behaviour but he says he doesn't want to go on holiday again/spend the money on a foreign holiday if it's going to be like this. This time has definitely been the worst - is this because he is going through puberty? I don't have bio kids of my own and sometimes find it hard to know what is typical of any family anyway and what is different because we're a "blended family".