Issue with self service after upgrade

I’ve just upgraded my RT installation from 4.2.10 to 4.4.1. The upgrade proceeded withouth any errors and warnings, however I discovered an issue. Before upgrading, we used the RTxAssets plugin (which has now been cored), and we had granted users the right to modify certain custom fields. After upgrading, we discovered that the users are no longer able to modify these fields via the SelfService, even though we’ve verified that they have the correct rights set.
Can anyone help? – Thomas