Moving/zooming composite track of line/area features

[Marlin-Na]

Dear Miguel,

I have reproduced an example reported at Marlin-Na/TnT#4 that the composite track of two line tracks is not animated correctly when moving and zooming, which is at http://bl.ocks.org/Marlin-Na/63c1f2bd7f727c66f931e97c40104163 .

When moving or zooming, it seems that only the last track is moved, but oddly with color of the first track. After zooming or moving, the tracks are again rendered correctly.
It seems that the behavior only involve composite track of line/area tracks.

Can you have a check with that and do you have any idea about possible reasons?

Thanks!