It depends what you've got on the branch, yeah - the ideal is that you pull request the branch, and then it merges smoothly. If you've got branch A, then you branch B off it, then C off that, and C gets merged, then A and B will go smoothly. But if you did an extra thing on A that's not on C, then it won't go, which is the whole aim.

Can you point me at an example branch? It's easier to explain with diagrams and commits to refer to.

I'm not quite sure how to explain about pull requests, because I got so familiar with them that it's hard to break it back down. Which ways are you looking at? It doesn't matter so much which button you press as what you're requesting from and to - there are several ways to achieve the same thing.