(also in version 4.2.6 which the bug form won't let me put)

Adding a new trigger to an existing template and then attempting to make this trigger dependent on other triggers in the same template fails with:

"Cannot add dependency from a host to a template."

The template has other triggers with dependencies on triggers in the same template, so the clearly is (or used to be) possible.

It also fails if adding the dependency as part of the process of adding the trigger (instead of trying to add the dependency after the fact).

My guess is:

The update process is failing to transform "template name: trigger name" into "host name: trigger name" when iterating through existing hosts.

This seems similar to or the same as the issue in ZBX-16122, except in this case, the "other" template is actually the same template.

Also, attempting to follow the link to the fix results in:
"No branch, tag or commit 'refs/heads/feature/ZBX-16122-4.0' exists in repository 'Zabbix'"