I configured an URL into a trigger configuration (let's say: http://somesite.com) .
If I click to the trigger name in Monitoring -Triggers then choose URL in popup while it is in problem or just resolved, the final url is http://somesite.com/?sid=1234567890abcde
I think this gets done to work with frontend related hyperlinks.
Fixed in svn://svn.zabbix.com/branches/dev/ZBX-7634 r41493
Fixed in 2.0.11rc1 r41497