I am changing the font size of the choice from another another choice after selecting the item. but the font size is not changing immediately.

Step to reproduce:
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1) Run the attached program.
2) Select any item from the first choice,say 10. Observe that choice two remains the same.
The font size changes only when second choice is clicked to see the items( drop-down).
This works fine in MToolkit. It even works in Mustang b20 , but fails in Mustang b30 onwards (XToolkit is introduced).
I tested this in mustang b104 & Dolphin b04.