In Object mode, objects scallop away as I zoom into the scene to work on the object and disappear. 
This only started today as I worked on the scene. I duplicated a small sphere, changed the material and texture, back and forth between Edit & Object modes. I go in for a different angle and… see the picture, please. Camera view is just fine, and I could continue this way but it’s not addressing the issue. I hope someone can steer me in the right direction! Thanks for all you help, having lots of fun trying to learn all I can here!
It seems to be related to the center mouse button. If I pivot around the object and wheel in, this is when it happens.
If I use the # keys to move I can get in as close as I want. This is only in this file, so something, somewhere in this blend is doing this?!?