The field values the user has modified in bulk edit issues are lost (not loaded) - however the correct checkboxes are selected

Steps to reproduce:

1. create issues...
2. bulk change all/some issues..
3. choose 'edit issues'
4. change some field values (eg. enter a comment in)
5. submit (to goto step 4: confirmation)
6. go back to step 3 (the comment is not there, but the comment field checkbox is selected)