[Typo3] sr_feuser_register - multiple select

[racco]

hello,

I was struggling to get multiple select to work, but I failed, I do not 
know what is going on.

So this is my situation:

for multiple select field I get the values from foreign_table
multiple selection input field is displayed correctly, it remembers its 
selected fields during registration
on preview screen I can see the names of options I have choosen, so it is ok
everythings breaks down when it come to save, although it is said that 
my account was created, the values from multiple select are not in DB
so edit displays nothing
when I add this selection through BE, then in Edit mode it is ok, I can 
see my selected options, but when I try to save, this data is lost

my template, hidden fields - I use [] brackets to indicate the multiple 
character of this select input ( [fe_users][fieldname][])
when I tried to do this without last pair of [] my preview worked, but 
after clicking create it was turning back to form with error message: 
Fill in fieldname (because it was required)

I believe there is either something wrong with my configuration or with 
writing to DB. Maybe this JS function at the end of class has something 
to do with this, I do not konw


hope u can help me


racco