Text in multiline TextBox disapears when using TabControl

[Adagio]

For the past 1½ year there hasn't been a problem, but last Friday I made a change to a program that is being used by a lot of people and sent out an update. The only change I made was to add a TabControl, and move all the controls from the form into the first tab-page (second tab-page still empty)

The two multiline TextBoxes I have on the form now has a problem: Unless there's focus on one of the TextBoxes, the content is "cleared" (well, the text is still there, but you can't see it)

I remember I had this problem myself on some other form (a form that is only being used on my computer at present time. This form also has a TabControl), but I haven't seen this problem for a while (and I don't remember doing anything special)

Does anyone here know what could be the cause of this problem?

 

[Adagio]

The error also happens on one of my colleagues machines, where VS is installed. Should make it a bit easier to find the problem, but so far without any luck

 

[Adagio]

I added this code:

TextBox1.Invalidate()

On TextBox1.MouseLeave and MouseEnter events

Initial results showed that this took care of the problem. Not the best solution to the problem though, but better than nothing