Two consecutive blanks does not work in "drag and drop into text" question type in 2.3.
The [[1]] and [[2]] [[3]] sat on the [[4]].
Choice 1 black
Choice 2 white
Choice 3 cat
Choice 4 mat
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When previewing question, it's impossible to drag choice 2 (white) into its box.
However, clicking "fill in correct responses" does work.
Note this bug was apparently introduced in current Moodle 2.3dev (Build: 20120601).