How to reproduce:

1. clone a graph from a default template, e.g. CPU load
2. rename and uncheck the Show legend option (that is the only difference)
3. add this cloned graph to a screen using any host from that template
4. make sure the Dynamic item option is checked
5. view the particular screen in Monitoring -> Screens
6. graph should appear with no labels as expected
7. change the host in top right dropdown
8. notice that the legend is shown again even if the graph was templated and if the same hot was selected