These are all to do with the combination of the $form->category, and $form->categorymoveto fields on the question editing forms since Moodle 1.9. These are now resolved to a single ->category value in question.php, which simplifies the logic for the individual question types.
MDL-15774 and MDL-12719 errors editing Cloze question
MDL-17105 problems with qustion saving logic.
MDL-18174 'Select from subcategories' option not preserved when editing a random question.
In the 1.9 branch this is controlled by a new option under Admin -> Experimental. In Moodle 2.0 dev it is not optional, it just works.
The main change is letting the manual grading report know which random questions might need manual grading. MDL-4004 - this depends on the random question under consideration, which requires a new questiontype method.
I also changed the random question code so that I could remove some global variables.
All the credit goes to Paulo Matos who carefully worked out and tested this fix, and updated the patch several times over more than a year while I very slowly got around to reviewing it and checking it in.
* Don't let the user set the name for random questions.
* Instead force the name to be "Random (catname)" (localised) whever the question is created or saved.
* When a category is renamed, rename all the random questions in it.
* Remove the restriction that Jamie seems to have added in 1.9 that was preventing the category of random questions from being edited.
If there are any of the files styles.css, styles.php, script.js or script.php in the plugin folder, they will be linked to in the head of the quiz attempt page (only for the question types used on that page).
If you need to do something more complicated in your question type, you can override the get_html_head_contributions method instead.
While implementing this, I removed the ~100 lines of very similar code from the top of each question type's editquestion.html template, and moved this to a the function print_question_form_start() in the base class, which uses the template question/type/editquestionstart.html. This is described in more detail here: http://moodle.org/mod/forum/discuss.php?d=51590, and is why this patch makes the codebase 523 lines smaller.
