VMG4927-B50A in bridge mode disables admin login

mss1911

I've been using the VMG42927-B50A stably in bridge mode for a year now, (It is the DSL bridge to a Mikrotik router which is the backbone of my homelab) and overall it does its job quietly and without complaint, and I have no issues. Except for one minor nagging complaint:

Once the Zyxel is put into bridge mode, GUI admin login becomes disabled! I can only re-login again by doing a factory reset. The GUI login webpage at 192.168.1.1 does, in fact, load just fine in my browser. But using "admin" and either the default password (or one that I reset it to), it fails the login with "Incorrect password" every time. It doesn't seem to be an actual incorrect password issue though. It's not a captcha issue, and it's not an issue of plugging into the correct ethernet/LAN port (I've tried them all). I understand the web interface login is disabled when a telnet session is in use, but that's not the case. In fact, telnet and ssh time out if I try to log in that way (nmap reports that ports 22 and 23 are filtered). My firewall is permissive for these scenarios, so that's not the issue either.

99.9% of the time, I have no need to log in to the device, so usually this isn't a problem. But once in a while, I need/want to log in directly to check some network diagnostics as close to the source as possible. And if I wanted to reconfigure it out of bridge mode without resetting the device, I'm out of luck. It's annoying to have to factory reset and re-configure it just to login, for multiple obvious reasons…

Is this intended behavior, that admin login is disabled when the device is in bridge mode? If not, is this a known issue? Is there a firmware update that addresses this? Am I overlooking something silly? I searched the device manual but found no clues.

Thanks!