Google view frustrum and check it out.
It looks like a graphics issue from the quick search I did.
Maybe a tweak of your Preferences>Visualisation Performance Preferences and hit the "Evaluate Graphics Performance" Button.
There's also a tick box under the "Large Model" Tab that you can turn "View Frustrum Culling" on or off. I'd try and turn this off if it's on or vice versa and see if you have the same problems.
Hope that helps.
Thanks Mark. That suggestion put me in the right direction. The "Large Model > View Frustrum Culling" was OFF, I turned it ON. Also, under "Visualization Performance > General Settings", I set the "Repair Wireframe Erasures" to "Wireframe View Only" (was "All Views"). After running the "View Update" all went well. For grinns, I also ran "Part Clean-Up" and saved the file. When it reopened, all was fixed.
Thanks again for the help.
Taz