Simplest way to reproduce:

• create a template with one dummy item;
• create a trigger with name "a" for this item;
• create a trigger with name "A" for this item;
• sort triggers by Name as ^;
• open another browser tab and edit those triggers (in two steps) to get swapped trigger names;
• make sure that sorting is set the same way as on previous tab - as ^;
• compare with previous tab and notice different order of displayed triggers - reproduced.

In such case triggers actually sorted by trigger ID.

There could other use cases to reproduce it - like host exporting and then importing with different name etc.

A patch to fix it:

Index: triggers.php
===================================================================
--- triggers.php        (revision 58503)
+++ triggers.php        (working copy)
@@ -490,6 +490,7 @@
        $data['paging'] = getPagingLine($data['triggers'], $sortOrder);

        $data['triggers'] = API::Trigger()->get([
+               'sortfield' => $sortField,
                'output' => ['triggerid', 'expression', 'description', 'status', 'priority', 'error', 'templateid', 'state'],
                'selectHosts' => ['hostid', 'host', 'name'],
                'selectDependencies' => ['triggerid', 'description'],

With the fix - trigger "a" will be always first, as it is for example for item keys in items list, or order of entities in exported XML - lowercase letters are first.

I supposed this bug could be fixed by ZBX-9402, but it's not.