Does anyone ever had a problem with a Sears riding mower blade disengagement?

No, what are you having a problem with it disengaging? Electric or manual?

I actually had a problem something like that after the mower was used in very tall grass it stretched the belt ( I guess) and it would disenguage every time it was stressed I ended up buying a new belt and it worked fine

I have a problem with a Craftsman, made by AYP, that is similar. Your question may help. My blades would disengage after about 30 minutes of use. The problem started after I replaced the belt. Now it will not engage at all. I am wondering if we have the same problem. The belt may be getting stressed because it will only work a short time. Then the blades would not engage at all. Maybe I have a belt problem.

Did you check your switch, in your earlier posts, you said you did not hear the click from the pto clutch anymore. And yes you can have a stretched belt and after running for a while, it will get hot and stretch a little more.