This has me baffled. The system is a KXTDE200. Extensions are KXT-7633

One extension is acting weird. It can place and receive outside calls just fine, and the DSS lamp for that station lights when it goes off hook. But when you place an intercom call TO that extension the extension''s DSS light does not come on.
The extension auto-answers like it should, with the alert tone, and you can talk to the extension, but there is no audio coming back from the extension. I tried 790 clear station features but no change.

I suspect some station 'feature' has been inadvertently enabled but I can't figure it out.

Any assistance is greatly appreciated.