Steps for reproduce:

1. Create template ? 1 in this case Template App MySQL define items and graphs, first screenshot.
2. Create template ? 2 link it with template ? 1.
3. Create Host and link to template ? 2.
4. Do some changing in template ? 1. Second screenshot, And save it.
As a result have third screenshot.

If you want to do this changing, remove graph and re-create.
Also need DM, nodeid > 91.