Howdy and Welcome...
I just want to point out that you might be better off with three frame setup rather than two frames in that case...
The first frame sets the value, and go to the second frame when all the items gets populated, and the warning message on frame three returns to frame 2 rather than frame 1...
Store the selected value on that combobox component with getVaule() function, and when you are returning back to frame 2, reset the combobox with previously saved variable with setVariable() function...