I'm curious about why your students have the screenreader setting set to yes if they should see a visual drag-and-drop question in a quiz. (The idea behind the check is that students using screenreaders get something that looks exactly like the original matching question while students who can work with the visual drag-and-drop interface see something spiffier. Both versions are totally equivalent to the original matching question grading-wise.)
I'll admit that I'm not familiar with much in moodle outside of the quiz. Is there another module where screenreader=yes does something useful/interesting for users who are not visually impaired? Is it not possible to ask the users to change this setting if they don't use a screenreader and want to see the drag-and-drop version?
With the imagetarget question there are two problems with the screenreader check:
1) there is a bug in the screenreader check, so it currently doesn't check anything (as you noticed), and
2) when looking into it the other day, I realized that it doesn't make sense to give screenreader users imagetarget questions at all (the check is only there because I copied it over from ddmatch), so I'd be in favor of removing the check rather than fixing it.