For everyone interested..
I made several experiments, and I found out that the issue happens only if the wifi connection is teared down from the user.
It doesn't happen if the connection is severed from AP side, for example. When the AP is restored the association is renegotiated almost immediately and works fine.
Very, very strange.
I'm pretty sure the problem is not in wpa_supplicant, because it works fine if I don't use the onboard wifi (for example using an USB wifi dongle);
it must definitively be something wrong/missing with the 8189es driver
Nevertheless, there are several quick workarounds.
For example: don't disconnect from nmtui or wpa_cli, use ifdown instead.