I have seen an unusual error, and was hoping someone might could explain the cause.  When you normally open an assembly you see in the design tree the main assembly at the very top, followed by a list of tree items depending on your individual settings (History, Blocks, Equations, Planes, Origin, etc).  Then you would see sub assemblies and parts that were within the main assembly.  I am finding that sometimes when I open files you see the main assembly at the top of the design tree followed by all sub assemblies and parts, and then the typical tree items listed below those.  The parts seem to behave normally, except when you try to save you get "an unknown error".

The only way I have found to fix the problem is to add a new part (which will appear below the tree items in the correct position), and then drag every other item back down below this one.  Except sometimes parts disappear in this process.  I have noticed they remain in the history folder and seem to remain in the assembly although they do not appear anywhere in the design tree.

I am using SW2014 SP 4.0.  Has anyone encountered this error before?