Okay, after researching the subject, we finally found out what the issue is in some browsers:
http://stackoverflow.com/a/9514875
We patched our code to follow what described in that article, and according to our tests, it is working as expected now.
Those of you who want to test version 3.8.1 before it's officially released here on the WP repo, can download it from our github repository
https://github.com/getusedtoit/wp-slimstat/releases
Cheers,
Camu