A lot of good comments here, and I think the OP stepped in it a little bit. It should have been a wee bit more obvious that the overlap was likely to cause some

A lot of good comments here, and I think the OP stepped in it a little bit. It should have been a wee bit more obvious that the overlap was likely to cause some concern, so chalk this one up to a professional learning experience, which as others have pointed out could have been a lot more costly. Another factor, imo, is that regardless of how supportive of open source your employer is, human jealousy and possessiveness still comes into play. Nobody is getting as much work done as they would like, and they never will. When a manager hears about an open source project I guarantee you some little corner of his or her brain feels like they want those hours for themselves. I've seen this emotion inadvertently aired on more than one occasion. If the project in question is truly a side project and truly unrelated then the manager's best course is obviously a held tongue. But it if is potentially competitive? Now the reaction has legitimacy, and for that reason alone it's best to steer well clear of anything that might be a conflict.