Unsupported operand types, line 51

This bug is reported in another issue (comment http://drupal.org/node/358617#comment-1416484) which is really about something else (bulk editing CCK fields) and which wandered all over the place, making it unclear if this particular bug is being addresses; so for clarity here it is in its very own issue!

When trying to add a new Modify Node Fields action at admin/settings/actions I get the following error:
Fatal error: Unsupported operand types in /usr/share/drupal6x/sites/all/modules/views_bulk_operations/fields.action.inc on line 51

I'm using the dev version (freshly downloaded 10 minutes ago, was using 1.7 before that which produces the same error). I'm working as user 1. Core version 6.12, CCK 6.x-2.4.