Listing description formatting lost on 6.5.5

Having upgraded from 6.3.1 to 6.5 it appears that the formatting in the listing description has been lost. By that I mean headings and paragraphs no longer show resulting in one long unformatted listing.

Has anyone encountered this and is there a simple fix? I dread the thought of:

a) Contacting every client and asking them to clean up their listing – so unprofessional.

b) Going through and correcting every listing 😯