4.2.6. The SNMPv2-Trap-PDU
... The first two variable bindings in the variable binding list of an SNMPv2-Trap-PDU are sysUpTime.0 [RFC 3418] and snmpTrapOID.0 [RFC 3418] respectively.
The Smarts trap manager parser, checks within the V2c traps that the first varbind is SysUpTime (".1.3.6.1.2.1.1.3.0"), and that the 2nd is the TrapOID (".1.3.6.1.6.3.1.1.4.1.0"). If this is not the case, the first test for sysuptime fails, and an exception is raised which causes the packet not to be parsed further, resulting in the packet being discarded.
This RFC requirement is specific to V2c (V1 is not affected).