I had this issue when I had multiple questions in one field list and one of
those questions determined if a later question within the same field list
would be relevant.
E.g. Imagine the below scenario.
Begin group (field-list)
Q1. Have you ever eaten pizza?
Q2. Cool, what's your favorite toping? (relevant only if person
answered 'yes' to Q1)
End group (field-list)
Q3. Do you like music?
The only way I found to fix this (and there might be others) was to remove
either the independent (Q1) or dependent (Q2) question from the field list.
Otherwise I had your problem AND an added one: Even if I made Q2 required,
if I used my PDA and answered 'yes' to Q1, I was still able to skip ahead
to the next question (Q3) without answering Q2.
Hope this helps