This is caused by CR net0041652, this should be fixed in Extreme Management Center 7.0.4.
Some definitions in trapd.conf are duplicate and cause some trap definitions not to show up when you want to create a new alarm.
A workaround is to copy the entry you want to add from trapd.conf to mytrapd.conf and restart the Netsight service.
For example :cat mytrapd.conf
EVENT etsysMACLockingMACViolation .188.8.131.52.4.1.56184.108.40.206.1.0.1 "LOGONLY" Warning
If MAC Locking is globally enabled and specifically
enabled for this port, then this trap is sent when
a packet is received with a source MAC that differs
from all the currently locked MACs for the port
specified in this instance of the notification.