Contents of Form Fields not Visible in Ver. 6 but in Ver. 5

[FraDo]

Hi all,
I have received a PDF file in file format 1.6 which contains interactive form fields.
The strange thing is that I can see the fields' contents in Foxit Reader ver. 5.5.6 but not in ver. 6.0.5

How can this be?

Regards
FraDo