Hi Guoda,
The cache actually does not remember the the deleted image, only the space allocated, this is done in order to prevent fragmentation of the cached file, the space is 'Marked' as free and later on used by another image.
I am currently working on a shrink option to solve the issue you have described, I hope to add it to the current beta.
There is currently no way to change the location of the cache file but I will add that to.
Thanks And Regards,
Asaf.