JSON roundtrip doesn't preserve non-positional features

As per summary.
Example: uniref50.fa with exampleFeatures.txt.
Hide all but METAL (to avoid bug JAL-2543).
Check that File | Export Features to textbox includes non-positional feature on FER_CAPAA (feature start = end = 0).
Output to Textbox as JSON, select 'Export feature'.
New Window from textbox.
Turn on feature display to see METAL features.
File | Export Features does not include the non-positional feature.