There it is! A BUG in Visual Basic Express 2010:
I have several ToolStrip controls docked within several panels of a tabPanel.
And sometimes, some toolstrip disappear from the design page.
Still exists since I can see its name in the bottom under the design surface. If I click that name, kazaaaaam!!!, if shows back, but if I click another control elsewhere it vanishes again.
And after compiling and running the project, user can't see it neither.
Only solution is insert a fresh new toolstrip and copy/paste the bad one's buttons!
Any clue?