A quick add-on: my total trial time is 3000 ms (I omitted that part of the script), so it isn't a question of the trial ending immediately after the responsecue.
Have you figured out a solution to this problem? I am having a similar issue with the voicerecord attribute (i.e., super fast RTs that don't make sense).
It sounds like Inquisit maybe reacting to ambient noise from the microphone. To fix this, try setting the /voicekeythreshold on the <defaults> element. Increasingly higher threshold values configure the voice engine to react to increasingly louder sounds, ignoring sounds at volumes below threshold.
Here's the documentation on /voicekeythreshold:http://www.millisecond.com/support/docs/v4/html/language/attributes/voicekeythreshold.htm
Let me know if this helps.