CTabCtrl with CListBox, all resizable. How?

Hi there

I have a problem with the TabControl. I've created 3 tabs, each one with a listbox. They're on a FormView in a MDI-Application. So far, so good, that works fine. Now I have to make that resizable.

By now I get the rectangles, calculate dx and dy use the MoveWindow() function to set the new size. But that doesn't work properly. The listbox doesen't resize with each pixel (as the tab control does). Instead it resizes in steps of about 5 to 10 pixels. What could be wrong? Does anybody have another solution for this?

Thanks

Holi