"set dpd disable" doesn't disable DPD......

I have a 30E device running firmware 6.0.4. I have the following phase1-interface S2S config:

    edit "1176"         set interface "wan"         set ike-version 2         set keylife 28800         set authmethod signature         set proposal aes256-sha1         set dpd disable         set comments "VPN: 1176 (Created by VPN wizard)"         set dhgrp 5         set nattraversal disable         set remote-gw REMOTEIP         set certificate CERT         set peer "1176_peer"     next

According to debug logs on both the Fortinet and the other site (a Cisco ASA 5506), the Fortinet is still sending DPD messages every 10 seconds.

How do I fix this problem?