Steps to reproduce:

1. Changes in configuration... Nothing
2. Navigate to screen title... Latest data, select host, select 2 item (example "agent ping" and "ICMP ping"
3. Click on screen element... "Display graph", select View as Values
4. ... An element with value conversion has no data - it is converted to an incorrect value (in my case to "Down()" with an empty value). If you disable value conversion, it is displayed correctly.

Result:
See screenshot... In attachments
See log file...
See memory dump...
Expected:
See screenshot....
See attached patch file...