I’d not expect the downlink queue to be purged. But indeed, I’d also expect the network to recognize that it’s not a retry, so not repeat the previous downlink. That said: seems like an edge case, only happening for downlinks when the uplink counter is 1?
(Could still be troublesome, of course, especially if that very downlink would be some command to reboot the device. So, for that use case some special handling might be needed in the device. Same goes for accidentally using a confirmed downlink for such reboot command. And just to be sure: a device should not do an OTAA join very often.)