In the display where it says "calls holding 1" that is telling you how many calls are on hold. The number beneath it indicates which LINE is being held. Next time this scenario occurs make sure you press the numeric button that corresponds to the number previously described. I'm guessing you will get nothing again but at least you will know your in the correct place to retrieve a call from HOLD.

The most common reason for this circumstance to occur is that within the previous minutes there actually was a real caller that was placed on HOLD. Then the caller got impatient and hung up. Due to improper balanced settings within your system combined with noise on the line from the service provider the system thinks there is a real caller still on hold and keeps the line intact. Enough about that.

If this requires attention from the service tech (and it will) give him a hint to adjust the line settings. It may have been done already and hopefully the problem goes away.