I have noted problem with correct ranging of items.
When I have ranged stamps "Countries => All => Issued on" (100 items per page) and marked some issues then I could see these marked issues on next page.
I think it's a big problem, because it means that some NON-MARKED and NON-SEEN issues were moved to previous page... Isn't?
It's no sense to write link to page, because each time there is different picture, but it's possible to check it using "Mark all" on one page then go to next one and look on presence of marked stamps.
These problem can be very unpleasure, because when you go through 2,500 stamps to make full lists and later find non-marked issues