I noticed the same thing, I think this piece in the 5.0 GA User Guide may help :
[KNOWN LIMITATION] Currently the forms as worked out in Activiti Explorer do not yet use the submitStartFormData and submitTaskFormData. So the form properties are not yet archived when using the forms in Activity Explorer. A workaround is to set the historyLevel to full and use the variableUpdates to see what values were set in userTasks. @see ACT-294
