Normal Maps/Round Corners Attr with baked Lightcache rendering black

[jksim]

Hi,
I've been using the trusty Irradiance/Lightcache baking method for some large city environments, and I'm finding that when I use fly-through for the lightcache, I seem to be getting a LOT of what appear to be invalid normals/negative colours that leave large blackspots in my render. It seems that anything that alters the surface normals (the round corners attribute or normal maps in tangent space as a bump) at render time seems incompatible with the fly-through mode of LC? If I render single frame (unbaked) LC, I don't get any issues.
Any ideas/workarounds?

Thanks
Josh

[vlado]

Can you get me a scene where I can reproduce this?

Best regards,
Vlado

[jksim]

Unfortunately its a film under NDA, I'll try and reproduce it in a clean scene and send it on
cheers
Josh