You might be selecting a third invisible endpoint. If you select ONLY the two endpoints of the open curves then you will not have a problem. No need to release compound paths if the path is open and it is in fact an open endpoint.
@JETalmage, This thread is still helpful, 1. Not everyone have latest versions. 2. This was helpful for me, since his situation was about trying to connect 2 compound paths together, which woin't work unless you right click and release the compound path, which he stated earlier in the thread.