wiki rendering in work log excludes paragraph tags

The preview of a work log comment includes paragraph tags, but after logging, they are missing when the work log is actually rendered.

To reproduce,

1. start logging work on an issue
2. include a blank line between lines, e.g.:

   test
   
   paragraph
   

3. click the preview button
4. look at the HTML source of the preview, confirming paragraph tags
5. click the log button
6. look at the HTML source of the work log (paragraph tags are missing)

Expected result: the work log contains paragraph tags for text separated by blank lines.

Work around: use two pairs of double-backslashes to get a blank line in a work log.