virtualizationThreshold not working? and a bug when bigger then data list

Noticed when virtualizationThreshold is set to a larger or equal number then the data length, it will cause serious unresponsive lag. The plunker, which is a fork of issue #5585 (scroll lag), will have a hard time loading. The virtualizationThreshold is set to 1001, data list begins with 1000 and increases. When the data list is larger then 1001 it returns back to normal, with scroll lag.

https://embed.plnkr.co/wmxIyxz7GGQc1r8oytUf/

That's one issue, the other issue is that it is not working, I guess? As far as I know the virtualizationThreshold should render the amount of rows it is set to? Yet it seems it does not render more than is visible because it still shows white rows when scrolling (thus rendering new rows). I might be wrong here?