If you have a choice box with three items, where item two is selected, the selection menu looks something like this

   item one
✓item two
   item three

Now if you select item three, you would of course expect the check mark to move from item two to item three like this

   item one
   item two
✓item three

However, after selecting item three on my Mac and then clicking the ChoiceBox to open the selection menu again, what I am seeing is actually a short animation like this

at 0 milliseconds
   item one
✓item two
   item three

and at approximately 200 milliseconds
   item one
   item two
✓item three

So the check mark position is only updated *after* I open the selection menu again. Of course this flickering is not desirable, and I recommend changing this so that the check mark is relocated before showing the selection menu again.