I am working with a CTX-100 with digital phones. Starting about 3 weeks ago, extension 115 will call extension 100 by itself. The phone is back in the shop and sometimes there is nobody back there and it will call 100. Swapped phones and that did not help. If I leave 115 unplugged it still calls 100 and ties of phone. You have to pick up the receiver at ext 100 and hang it back up to get the phone working. The display on 115 doesn't show any type of call forwarding or message waiting set. No other lights set. Could it be a Call Return feature? I figured it would have expired by now. Doesn't happen every day, sometimes it will happen 5 times in a day. Weird, not sure what to do next.

Have you tried deleteing X-115 and rebuilding ?

We are a tosh dealer had same thing on are office system turned out to be the extn card dodgy batch it might do it 4x in a week then not for 9 months

If your bdku is a v1 then swap it out with a higher version.

Thanks for the assistance, I will try your suggestions and let you know what the fix is. Thank you.