Chainsaw Repair

I've never had a problem with the chain tightening and binding while cutting except when hitting water. I don't set the chain brake either. With the chain brake set with the motor running it may cause the chutch bell to bind on the clutch and heat up. I don't know how many hrs. your saw has on it but it may need some wear parts replaced. I would pull the clutch, lube or replace the bearing and replace the sproket. If the chain is mostly worn out I would replace it with two new chains. With the bar off I would check the sproket nose to see if it turns smoothly with out in and out play. I like to tighten the bar nuts tight enough that the bar can't move while cutting or pulling out of a pinch. If the bar nuts aren't tight the bar can move loosening the chain most of the time or in your case tightening it. Some bars I've seen will lock down the sproket nose with wood with a loose chain and the bar nose buried.
Billy