Missing Input Contactform 7 MultiStep

Hi,

I wonder if anybody ever had the same problem:
I am using the Multistep Contactform7 but sometimes I get mails with one empty inputfield – which is a bit odd, since its not possible to skip the input and send the mail without it.
I tried to achiev that a couple of times but that seems impossible – so I wonder what is happening.

Maybe anybody had a similar problem (and hopefully a solution too)

Thanks in advance!