No, Telescope doesn't cache previews, because they are supposed to be real-time, so it doesn't make sense to cache them. Telescope also doesn't remember which applications did you started.

So if the reason of that behavior is Telescope then it is probably a bug
Intent look at destructors of main classes in the sources doesn't gave me idea why this could happen. It seems that i free all resources accurately. But of course, i could have something forgotten.

By the way, Telescope doesn't deal with applications at all, it deals only with windows. So it would be interesing how it will behave if you will open several windows of same application (XTerminal for example).

I don't have my N810 near me at the moment. But i will test and try to fix this soon.