Well - the pattern seems to be that I see the phones in Windows Explorer but they're only there for a while and then disappear. They never as far as I know, appear as attached devices in the router admin page. Neither is there a trace there of the hidden IP's when I have found them with Netscan.
Although I previously used my PC on wifi, it's now connected by ethernet.
It does seem as if things only go awry if I enable wireless. So my answer for now is to keep it disabled.