That works great for all students for whom the problem has been assigned. HOWEVER, when using this bridge, students are not "assigned" the assignment until they have actually logged in and looked at the assignment at least once. If a student doesn't look at the assignment until AFTER I've marked it correct, then they will NOT receive credit.
As a workaround, I can be certain to assign the assignment to all registered users --- that way when I mark it correct all get the credit. Is this what I should be doing? Is there a better way? Is this the intended behavior?
I don't think there is a better way, at the moment at least with the current setup. For now it is the expected behavior. We may eventually be able to improve it, but it is one of the compromises we live with because half of the information (the user information) is on the moodle side and half (the set and user-set information) is on the webwork side. It will probably take a major database redesign to add the feature you mention so for now we have to live with the limitations of this "bridge1" between moodle and webwork.
The "bridge2" version (or question-server version http://webwork.maa.org/wiki/Moodle_Question_Type) in which all information is stored in moodle works somewhat better in this regard and the entire user interface appears as
moodle -- webwork is only used behind the scenes to process the problem.
In the long run this is probably a better model, but it's not yet perfect -- there are a few things that the moodle quiz does that are not a perfect match for webwork homework. However there is a lot of manpower being applied to the moodle interface and it's quite likely that it will eventually behave as a complete replacement for the webwork front end -- at least from the students' point of view.
We like posts! keep them coming :-)