I don't find it odd at all. Both my parents have accounts for the children. It's easier for them to stick money in if and when they feel like it.
Since they are contributing I think they can bloody well do as they please.

What I do find disturbing is that a relationship could be over on the basis of this kind of disagreement.
Yeah I kinda of agree... when they start playing around with money I have contributed towards my DDor DS's bank account then I think I'd get stroppy.

It is a bit of a worry though that your DP is blackmailing youw ith your relationship that way. I think when a couple starts a family, or even when a couple become committed, the parents of that child should always show a united front, if there is a disagreement then you should come to a compromise before having a fight infront of PIL/Parents otherwise there are going to be weak points of display that some people have no problem taking advatage of.

Just my two bobs worth GL, I hope everything pans out ok.