When you import a XAR page over another page which has already attachments that the new XAR page does not have, the old attachments are not deleted.
How to reproduce:
1/ Create a page
2/ Export the page
3/ Upload an attachment to the page
4/ Reimport the exported page
The attachment is still there while it should not.
This bug seems to be no present in < 2.4 (tested in 2.2.4 and 2.4) and present in > 2.5 (tested on 2.5.1, 2.7, 3.1.1, 3.3.1)