This is about accessibility, more precise, about navigating the page with keyboard.
Suppose we have the search option for combobox switch on. Using Tab key gets the combobox in focus. Then if we start typing, some options will fill the menu section of the combobox. Usinf Arrow keys (up and down) we can highlight one of the options. Using Space or Enter key, we make a choice of highlighted option. At this moment, the focus is still on the combobox and the menu portion is open. If we enter some more text and then press the Tab key, focus moves to Delete button of combobox, but the menu portion is still visible.
This doesn't seem logical, as we think the menu portion should be closed in this case.
Is our logic OK? If yes, can the behavior be fixed?