Steps to reproduce:

1. create a trigger or trigger prototype on the template level that depends on a host-level trigger and save it
2. try to open the host trigger form from the list or directly from the template trigger/trigger prototype form
3. the form will open successfully, but an incorrect "template" context is passed to this form
4. try adding another function to the trigger expression using the expression helper form

Result:
An error occurs when attempting to select an item:

This issue is reproducible starting from version 6.2.0.