Hi OrSol,
I cannot reproduce your problem. When you resize wlPanel , the combobox will became larger, but it is still smaller than userControl1. You can make userControl1 with a different color to see what will happen when you resize wlPanel.
When you resize wlPanel, according to the Anchor of userControl1, the size of userControl1 will be changed. When userControl1 resized, combobox will changed its size according to its Anchor.
Best regards.
Rong-Chun Zhang.