Tshark -w switch

Hi

I'm having problems using the -w switch with tshark command (V. 1.12.1).

If I use this syntiax: tshark -r "test.pcap" -Y "udp.port == 9090" I get what I want on screen (the output is correct).

Instead, if I add the -w switch tshark -r "test.pcap" -Y "udp.port == 9090" -w "out.pcap" The output file is empty.

Any suggestions? AF