Problems prepopulating form through url

Hi, I'm trying to populate a form based on information filled in in another form.

My first form sends an auto-responder e-mail upon submitting, and this e-mail contains the url to the second form. This second form needs to be populated based on the information in the first form.

This works perfectly for the e-mail field, but it does not for the full name field.

http://form.jotformeu.com/form/21063743269353?fullName6[first]={fullName3[first]}&fullName6[last]={fullName3[last]}&email={email4}

This is the link I use in my auto-responder e-mail. However when I receive the e-mail, the link is

http://form.jotformeu.com/form/21063743269353?fullName6[first]=&fullName6[last]=&email={email4}

It leaves out {fullName3[first]} & {fullName3[last]}.

When I send the auto-responder e-mail using normal data in the url, it is filled out correctly in the e-mail I receive

e.g. http://form.jotformeu.com/form/21063743269353?fullName6[first]=Sander&fullName6[last]=Mols&email={email4}

Is this normal? Am I doing something wrong?