moving average of eval-graphs incorrect when excluding old models

[amj]

Expected behavior:

When checking both 'filter bad' and 'filter old', the moving-average at the leftmost-edge should correspond to the moving average at that point when 'filter old' is unchecked.

Actual behavior
moving average of zoomed in window begins at artificially inflated number

Result: Upward trend obfuscated.

easier shown in pictures :)