Tested with git reset --hard badcc4866d88023102a3f72dc4f6f2193dec16b8
And a new installation :
Same think : http://205_dev.sondages.pro/index.php/survey/index/sid/337886/newtest/Y/lang/en

Only difference : Entering someting in text are not saved when click on a 'index' group.

The trouble with a full question index is that some compromises need to be made:

• If we validate questions we cannot save answers when navigating using the index. Since mandatory questions need to be filled in, validating them would deny navigation away from the page.

In my opinion the full question index should not save the current page when navigating using the index. This will provide the most consistent and easy to understand experience for the user.
Furthermore we might need some more documentation; the full question index imposes several limitations on the survey with respect to relevance equations / group relevance.

Not sure what the best way is to proceed. For 2.06 will need to rework the whole question index approach.

I think question index MUST save actual page. To have a button without save it's really a reverse or usuability (http://en.wikipedia.org/wiki/Usability).

In think the best is:

• Don't validate any group/question when click on #index, but save answers
• Validate whole survey when submitting

Please try and do a lot of different test with https://github.com/LimeSurvey/LimeSurvey/pull/227

Fixed here :
https://github.com/LimeSurvey/LimeSurvey/pull/227

This save value in DB but don't return error if there one.
AND the survey are rested just before submit

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=14619

Version 2.05 Build 141113 released