the easy way to know where the archivable flag is inherited from, is:
starting from HOME,
hover your mouse over the folder (in first case is home),
you'll see a yellow tooltip rectangle with some information in it.
if you read "archivable", that's where it comes from.
if there's no "archivable", move deeper in sub-folders, towards the folder you are interested.
before or later, you will see the "archivable".
if this method doesn't work for you, it's a bug or you missed it.
in such case, send your VFS to support@rejetto.com specifying the full path that should not be archivable but it is.