Hi Hosein,
Thanks so much for your report!
This is not a bug, because every item within “Nav items” is treated as a top-level item because the builder can’t know what should be a top-level item and what not.
You can manually adjust the markup as in your answer (in principle there should be no problems), or put the icon directly into the dropdown. Then, you only have to set the flex-direction of the dropdown element to row, change its gap setting and the flex-order of the icon to -1 and keep the actual markup (supplemented by the icon, of course).
Best regards,
timmse