I have a problem with some station labels I have, when I open the drawing(s) the labels display ??? instead of the station. After I manually sync the alignment in prospector, the drawing switches to the model tab with the ??? now showing correctly.
Yes, you've encountered the "you can no longer have pipes in an xref when the pipe network is also dref'ed into your current drawing" feature.
This "feature" was introduced in C3D 2012, SP2.1, and has now migrated to C3D 2013 SP1 and C3D2014. Do a search for 'does not synchronize' or similar search terms and you will find a bunch of posts by myself and many more by others regarding this. The only way I have found around this is to never xref my pipe drawing into my production drawings that need the Dref's. Yes, I had to change my workflows to do this, but it's workable....not so much with existing projects, although I just split up a project that's been under way for a few years to avoid this issue.