Steps to reproduce:

1. Create two host H1 and H2
2. For first host H1 create item I1 and graph G1 with this item
3. For host H2 create item I2
4. Create Graph (classic) widget and add G1 graph (or item for simple graph type)
5. Select option "Dynamic item"
6. On dashboard select second host H2

Result:
Not visible header. For other dynamic widgets (Plain text, Graph prototype) header is widget type
Expected:
Widget header "Graph (classic)"