The user interface editor in Visual studio sometimes gets confused when there are multiple controls on the form after controls are added, parented, and then removed.

There are only a couple of workarounds.

* Keep numerous backups and go back to a working copy when things go bad.
* Don't place controls on top of other controls unless absolutely necessary. Meaning --> don't place a bunch of controls where they ought not go... ie.) like a menu strip on a panel.
* Tabbed controls are pretty bad.
* Basically anything that is a parented control has trouble.

Why is all this the case you might ask???

Microsoft in an attempt to maintain backwards compatibility (and possibly to save money -- though I doubt that) ... used the old com controls in .Net (They are just wrapped up, but not very well done.) Lot's of bugs.

The tool strip and status strip are newer controls. Probably custom drawn with GDI+. They are mostly tested under runtime conditions. GDI code acts different in the IDE (during debug time) because the IDE tries to draw the control on the form even though a lot of initialization code is "skipped" during an interpreted pre compile phase.

So... that's the long answer. :) Hope that helps.
If it makes you feel better, it drives me crazy too. I wrote my own controls to get around the garbage that MS provided. The underlying framework is actually a lot better than the controls that they provided us.