Lika, I'm sorry, but there's something wrong on your side. Because we have a test installation on wamp 2.2. and wamp 2.4 on WIndows 7 and everything works fine. 

I talked to our developers,they told me there may be a lot of reasons why that occurs, browser settings, computer configuration and settings, wamp itself and they (browser, pc, wamp) may malfunction together. We can't tell you exactly what

Thank you

I think I found out why some people are having issues with missing fields.
In the join.php controller, when creating fake fields it generates a random key for each form field using

$randName = UTIL_String::getRandomString(rand(5, 16), 2);

The problem is that the function generates non-unique keys pretty frequently. So when this line is executed

$realQuestionList[$randName] = $this->questions[$sort]['name'];

There is a good chance that previous form fields are overwriten by a non-unique $randName. I don't know why that function doesn't seem to generate a unique key but just by echoing the form field name and randName you see something like this:

username randName : degYHENyg
realname randName :HERyHeMYPEWyTejY
sex randName : HERyHeMYPEWyTejY
birthdate sex randName :HERyHeMYPEWyTe

Results in a realQuestionList: Array ( [degYHENyg] => username [HERyHeMYPEWyTejY] => sex [HERyHeMYPEWyTe] => birthdate )

Quickest fix is to replace the randomString generator with the function that's used to generate a random id for the row css class.

$randName =  uniqid('ow_'.rand(0, 99999999999));

My join for works fine I tested it 20 times and since the new update 10 ppl have joined my site fine 

Yes, Guy, we were able to reproduce that on Windows server only, as our developers said this "issue" occurred due to some server settings, but they did not what exactly, as the a man who reported that was on local machine. However we tried to do the same but we could not.