Bridge keeps building thumbnails

Hello, 

Sorry for my novice question. 

I have added a folder as a favourite with a large amount of pictures in it. Every time I enter the folder, Brigde seems to be rebuilding all the thumbnails.

I think this has something to do with the cash.

However, I don't understand the difference between the cash settings that are a part of the Preferences and those available under the Tools menu. All checkboxes in the cash settings in Preferences are checked but this doesn't seem to solve my issue. Do I have to set the cash settings at folder level via the Tools menu as well?

Thanks,

Emmanuel