In EXOS 15.7 a fix is implemented (xos0056880) that only allows IGMP packets with a TTL=1.
In previous EXOS version every IGMP packet was excepted, no matter how high the TTL was.
If your device sends an IGMP packet with a TTL higher than 1 EXOS will not accept the packet as valid IGMP packet and not take action.
This is completely according to the RFC 3376.
RFC 3376 Section 4, Page 7
4. Message Formats
IGMP messages are encapsulated in IPv4 datagrams, with an IP protocol
number of 2. Every IGMP message described in this document is sent
with an IP Time-to-Live of 1, IP Precedence of Internetwork Control
(e.g., Type of Service 0xc0), and carries an IP Router Alert option
[RFC-2113] in its IP header.
Unrecognized message types MUST be silently ignored. Other message
types may be used by newer versions or extensions of IGMP, by
multicast routing protocols, or for other uses.