there is a BUG in Moodle 1.9 that affects WIRIS Plugin and other components. To summarize we can say that tags are broken by Moodle.
we have reported the bug and published a patch at Moodle tracker. http://tracker.moodle.org/browse/MDL-21721
We have solved the bug in our Moodle site for demonstration. You can check there if the problem persists. www.wiris.com/demo-moodle/
Pleaee vote for that bug to be solved.