Collapsing frame?

My home is a 10 year old oak timber frame. Over the past years I noticed the typical beam and joint shrinkage. However, there is one particular tenon that appears to be 'pulliing out' of its mortise. My family is frightened that the beam (which supports the roof and has no bearing wall) will colapse. The best that I can tell, there is approximately 1" of shoulder and the beam has pulled out atleast 1/2" to 3/4". There is a spline that connects the beam to others but it has split at the pegs. This is hard to describe. Can anyone recommend a course of action. I can take a digital picture and send it if anyone thinks they can help. Do I need a structural engineer? My timber frame contractor tells me that there is nothing to worry about but I doubt his conviction. I am despirate.