Had this confirmed by the local reseller after losing nearly a full day of work.
Working on a new project that was created in AC 9, using all AC 9 libraries.  Started a second session of AC9, both running at the same time.
The project I was working on had all AC 9 libraries loaded.  The second session was a detail 2-line drawing created in AC 8 with AC 8 libraries loaded but running in AC 9.  
In the first project file, I placed a detail marker.
Opened the detail marker and copied from the second session of AC9 the detail. So presumably I now have the detail copied into my detail marker in the new project.
Saved my work and continued the same process for another 50 - 60 details.  
Opened up details as they were placed to check on my work and everything was great.
I saved after each detail was placed as I hate to lose work.  Closed down AC to work on other stuff, and made sure all my work was saved.  
When I restarted AC I got an error message stating that some bad parameters were deleted.  i never got this message while copying nor saving when working on the project, only got the message when restarting AC.
When I reopened the project file, and opened the detail marker(s), all the 2d linework was missing.  Turned on all layers, but nothing in the detail marker.  Even though I hit save and checked my work as I was going along.
Here is the bug, and I can recreate it all the time.
The project file that I was working in was created in AC 9 and had all AC 9 libraries loaded.  The detail that I was copying into my project file, even though saved in AC 9, had AC 8 libraries loaded.   In effect, coping information from a PLN that has AC 8 libraries loaded into a PLN with AC 9 libraries loaded.  Note, I am copying versus converting.
To test if this was the problem, I unloaded all the AC 8 libraries from my detail file and reloaded AC 9 libraries.  All worked great.  Did about 10 details and each one worked perfectly.  Shut down AC, restarted, etc and all worked fine.
The bug can be recreated each time I copy a detail from a project that has AC 8 libraries loaded into a project having AC 9 libraires.
The local rep confirmed this could be a bug.  Would be nice if GS tested this as it cost me a lot of time and frustration.  
Grant