The App-ID cache feature in Palo Alto Networks PAN-OS before 4.0.14, 4.1.x before 4.1.11, and 5.0.x before 5.0.2 allows remote attackers to bypass intended security policies via crafted requests that trigger invalid caching, as demonstrated by incorrect identification of HTTP traffic as SIP traffic, aka Ref ID 47195.
https://security.paloaltonetworks.com/CVE-2013-5663
http://researchcenter.paloaltonetworks.com/2013/01/app-id-cache-pollution-update/