When I create a second trigger for an item that already has a trigger and is disabled, that trigger produces alerts. This second trigger uses the nodata check. For example if the item for the trigger

{Template_Linux:net.tcp.service[imap].last(0)}

=0

Is disabled then adding this trigger

{Template_Linux:net.tcp.service[imap].nodata(86400)}

#0

Results in emails coming out. I've had this happen with a number of items. The solution is to enable the item, wait a minute or two then disable it.

It's an irritating bug.