If you enter in a mask with the combo selected value to an item with index > 0 and choose the first element (index 0), the event SelectedIndexChanged doesn't fire.
If you select another item, differente from index 0 and then the first item .... SelectedIndexChanged fire!
If I understand correctly, you mean that if you fill a B4XCombobox and then "select the first item" that already appears as selected, the SelectedIndexChanged event does not fire.
It is normal, no bugs, since the selection has not been changed.
You can simply call the event directly, the first time:
No Luca. When I enter there is selected the second or the third or any other element (not the first). The first time that I select the first element (not previously selected) the EVENT DOES'N FIRE.
Make a test ... It's simple! The event doesn't fire.