After updating Moodle 1.9.19 to 2.2 and then to 2.3.2 all assignment descriptions appear in "Moodle auto-format" in the editor view. The result is that no HTML-editor is loaded (see screenshot).
The formerly type in 'assignment 2.2' doesn't matter. It doesn't matter if I run the assignment upgrade or not: The HTML-editor is missing, and HTML-tags are shown as plain text in the input area.

Researched so far:
1. Saving an assignment (updated or not) in 'HTML format' (chosen from the dropdown menu below the description input area) brings back the HTML-editor when editing the assignment again.

2. In the database table 'mdl_assignment' the value for 'introformat' is set to '0' instead of '1'. After updating the database (UPDATE `moodle`.`mdl_assignment` SET `introformat` = '1') the HTML-editor is loaded correctly, when editing an assingment.