Bramble Crumble with Custard / Bramencrumble met custard

So bizarre. You have brambles (we had really nice, expensive ones!), you pour custard over it, then top it with crumble and bake. What happened is that the crumble (which was perfectly fine, mind you) began to curdle and mixed with the crumble dough, which in turn didn't bake properly and wasn't done even after an additional 10 minutes baking time (on top of the original 20 minutes). It was a complete mess! Does anybody have an idea what happened? My suspicion is that custard isn't supposed to be baked. I mean, there is a reason why you shoould be careful not to bring it to a boil.

And it was such pity. The brambles were brilliant, the custard was nice, it would have been wonderful if we had just served the raw brambles with the custard. And perhaps baked the crumble seperately.

Edited to add: Done some research. So, apparently, a custard may curdle if it has been cooked for too hot (definitely the case here as it shouldn't exceed 80°C and the given oven temperature was 200°C) or too long. It may also curdle if it contains hot acid, which is the reason you shouldn't heat a lemon custard once you've added the lemon. And now guess where baking brambles gets you? The brambles get hot and release their (acidic) juices. In other words: this recipe was doomed to fail. How can this ever pass testing? Do they actually test the recipes properly?