I saw that someone else already complained about this, and you already responded, but you didn't mention what the fix was or where I could find out how to fix it.
I'm using CleanMart 3.3 in VM 3.0.8 + J3.4.1, and category descriptions seem to only show up for categories which have subcategories. If I rename the com_virtuemart override folder to com_virtuemart1, the category descriptions do show up correctly, so I believe it's your override file(s) creating the problem. I didn't see any switch in the flexible plugins.
I also notice the same problem for related products with your override files active.
BTW, this post says the most recent version of CleanMart is version 3.2, but I just downloaded a copy which claims it's v.3.3:
www.flexiblewebdesign.com/forum-virtuemart-2-template-support/1379-cleanmart-updates-check-and-request