Steps to reproduce:

1. Create a template
2. create a dashboard
3. Create a single page
4. Attach a `Graph prototype` widget , showing `SNMP Interface Traffic` in my example, but any data set behaves the same
5. Attach the template to a host
6. View the Monitoring>Hosts>Dashboard adjacent to the host > click on the page> view the graph `Interface: Traffic`

Configuration:
This is the configuration of the Widget:

Result: 

Note: I clipped the bottom chart off this picture, as it had a client-name in the interface description, i'm not permitted to share this.

Expectations:
The 'legend' is checked in the graph_prototype defintion, therefore this should be visible on ALL graphs.
The 'legend' tick has automatically included the associated triggers; whilst i never asked for this, it's a great thing to be able to toggle on/off.  So maybe expand on this by adding a 'show triggers' button in the widget editor.