Like almost any field mine has many sub-groups, not all of which play nicely together. There are dozens of reasons for the clustering and there doesn't tend to be a large amount of mixing over time. Perhaps the occasional one-off paper or collaboration, but they are few and far between.
As a trainee, I grew up on a certain side of the perverbial fence and continue to work with members of that group on a regular basis. For a variety of reasons, however, I can no longer be quite as active a member with that group and I have struck out on my own to a certain degree. As it were, this did not go unnoticed by others.
I should also mention that I am a fairly social person and have spent more that a few hours at conferences or pubs with a good number of the people in my field, regardless of their group allegiance. I rather like the discussions that occur between the groups, because it is extremely interesting to hear people lay out their arguments in a late-night discussion rather than in print after being sanitized by review. It's also a type of networking that I happen to be good at, for better or for worse.
Given the above, I guess it shouldn't have been that surprising a few months ago when I got a call from the head of a group I have had little 'official' interaction with i the past. I was invited to join a project that is in the early stages, but is quickly gaining steam. As things have moved forward, I now suddenly find myself involved in a least one major and a few minor publications as well as a grant application, which could greatly enhance some of my other efforts. Whereas this is a good thing for my personal advancement, I now clearly have a foot in different projects being driven by very different groups. While this isn't exactly a conflict of interest, it will be interesting to see how my new collaboration is viewed by those who I might consider to be my people.
It's a thorny issue that I am not sure how to navigate other than being completely honest with all parties about my collaborations and intentions. If I tread lightly, I am hoping to benefit from working in both circles without having either of them close me out. Hopefully I am not being naive as to how this will all play out.