route lines are drawn simultaneously

[mkandulavm]

Hi

I currently have route lines as a separate mbtiles.
When I use this, the coarser (low res) route lines of previous zoom seems to be getting interleaved with current zoom.

Please see this image.

Is this supposed to happen ? Is there some parameter to be set to avoid this ?
Can I get some hint where in the code (TileManager.cpp?) this logic might be getting processed so I can debug further ?

I have checked the yaml style and can confirm there is not duplicate layer.