Interference between 2 ComboBox

[Magic_Doctor]

Hello,

Here is a small program.
It works almost, if not there some kind of interference between the two procedures ComboBox.
When choosing an item in the first ComboBox, the result is almost instantaneous, then it starts to calculate something or other.
When choosing an item in the second ComboBox, the result is also almost instantaneous, and, oddly, the first item in the list required ...
I tried to hack a shorting ComboBox without success.
On the other hand, when the workbook is closed, the closure is not immediate because the calculations are done and I wonder why.

A very big thanks to help me.

[Magic_Doctor]

I come back on the thread.
Who knows, maybe someone will find an explanation.