I get rebuild errors on some piping every time I pull up my assembly out of the vault?  It is fine when I check it in.

It is simple piping going between two pipe fittings, straight pipe I pick the outer diameter one the start and then drag the route line to the other center outer diameter.  I was told to change the pipe to float afterwards.  

my steps are, I start by putting in pipe fixtures (tees and elbows) I locate them where they go and then use start at point to create the pipe and chose the correct pipe dia and click the outer dia and check twice and drag the end route to the other outer dia and done. 

I save every thing into the vault and check it in and go home and when I get back the next day and check it out I have a rebuild on the piping.