Wireless Networking → Unwanted AP activity from a client bridge?

After 10 years I'm still a novice at this, but I've managed to keep a home network running for internet access. Lately we have an ASUS router connected to a cable modem, with one wired and several wireless clients. One of the wireless clients is at the fringe of of the router's coverage, using an old Linksys ethernet bridge plugged into a desktop PC.
Last week that ethernet bridge died. Even with a directional antenna, reception had been spotty, so I replaced the bridge with an Engenius ECB-150 multifunction device (which has a more powerful transmitter) running in client bridge mode. It worked very well for that PC, giving much more solid wireless connectivity to the router. Then the problems started.
Other PC's within the house started having intermittent loss of connectivity. It seemed like wireless intferference until tonight, when I discovered that the computer that is hardwired to the router could not connect either! Trying to sort things out from the wired PC, I tried to access the router's configuration page at 192.168.1.1, and instead got the login page for the ECB150! (yes it's at the same address). When I powered down the client bridge, everything went back to normal.
So it seems that the client bridge is also acting as an access point, and devices in the house are connecting to it (even through the wired router) instead of the ASUS. How can that be ... isn't that the opposite of what a bridge is supposed to do?
More important - how can I fix this so that the ECB150 only works to bridge the PC it's connected, as the old Linksys did? Would appreciate any suggestions - thanks!

I suppose one way this could happen is if the bridge's own IP was the same as the router (192.168.1.1). That could create havoc; the ARP tables among various clients might try to use the client bridge rather than the router as their default gateway, and there goes your internet access. Hopefully this would be detected by ARP and reported (you know, that message you see in Windows when there's a duplicate IP on the network). And if the device has a DHCP server, disable it as well.

That makes sense. I didn't think a client bridge would be the device that assigned IP's to clients; it should be the DHCP server on the router with the bridge simply acting as passthrough.

As for the bridge sharing its base IP address with the router; I will see if the configs allow me to change that in client bridge mode.

Thanks for the suggestions.

Followup. I reset the base IP address of the client bridge to move it out of the range of the router's DHCP assignments. No more interference. Thanks for the help!