Found exactly the reason of the bug:

The parsing is right.
But when it insert the new row into the existing label table, the value is set in this manner:

value=" + value + "

So, because the value have a ' " ', we get this as a result with the string ' a"a '

So we have:
<input type="text" size="100" class="answer" value="a"a" id="answer_en_1_0" name="answer_en_1_0">

To fix this, the script need to escape the ' " '.

The user can't use the special HTML escape character &quot ; to fix this because the ";" is used by the parsing to set label code.

PS: The file is answer.js, not subquestions.js

The quick and dirty fix:

Line 614 of scripts/admin/answers.js :
Replace ...value="'+thisrow[parseInt(x)+1]+'"...
With ...value="'+thisrow[parseInt(x)+1].replace('"', '&quot ;')+'".....

I hope I helped

EDIT: I separed &quot and ; because if I join them together, the browser will show the " character.

Hello Damian,

thank you for the suggested fix. I see no general problem with it.
Since the editor for subquestions is very similar can you maybe please check out if it has the same problem and fix it there. too?

You should also in general get a GitHub account and submit the fix(es) as a pull request. Please also have a look at out standard for Git commit messages: http://docs.limesurvey.org/Standard+for+Git+commit+messages&structure=LimeSurvey+development

Any progress?

Yes, but I'm busy this week like I said in the mailing list.

The patch is done, I just need to commit it and do a correct pull request

Sorry for being so late

?

Damien, this was almost two weeks ago. Can you give us a status, please?

Sorry, I'm busy these days. I will attach the patch here tommorow but I think I won't have time until next week to do the pull.

Related pull: https://github.com/LimeSurvey/LimeSurvey/pull/64

Sorry for the delay. Thank you very much for the patch.

Fix committed to master branch: http://bugs.limesurvey.org/plugin.php?page=Source/view&id=11681

New version released.