Steps to reproduce:

1. Create a graph of items being monitored on a host.
2. Change the "Draw Style" to anything other than "Line"
3. Press the Add button to add the graph.
4. Go back in and edit the graph and the "Draw Style" will be line.
5. The graph items are always line and display as line when viewing graphs.
6. If you select the preview tab, it previews correctly, but always saves as line.

Result:
See attached screenshot...