Photoshop: 1000px feather radius does not apply in scripts

I've seen this post here: https://feedback.photoshop.com/photoshop_family/topics/larger_feather_radius which says how the selection feathering radius was turned up from 250 to 1000. I've confirmed that this is the case when using the GUI.

However, when trying to do the same thing via scripting, either using the DOM or using the output of ScriptListener, values above 250 give the same visual result as putting 250 (and thus, different from when entering those values in the GUI).

Specifically:

app.activeDocument.selection.feather(new UnitValue(amt,"px"));

and

var desc1 = new ActionDescriptor();
desc1.putUnitDouble( charIDToTypeID( "Rds " ), charIDToTypeID( "#Pxl" ), amt );
desc1.putBoolean( stringIDToTypeID( "selectionModifyEffectAtCanvasBounds" ), true );
executeAction( charIDToTypeID( "Fthr" ), desc1, DialogModes.NO );