IR map question

[palosanto]

I'm rendering a scene to a very large output (8000x4500) for a trade show large banner.
I've generated and saved the light cache and IR map at about 1/3 of the size prior to rendering full size using these saved lighting information files.
However, while the light cache file is read instantly, I'm still getting fairly time consuming IR "Prepass 1 of 1" . Why is it still doing a prepass, shouldn't it go straight to the rendering phase since it's read from the IR file saved previously ?

[Micha]

Did you use a material with reflection interpolation? If yes, this is feature cause a IM recalculation.

[palosanto]

Did you use a material with reflection interpolation? If yes, this is feature cause a IM recalculation.

Thanks Micha. Yes, there was one material with interpolation. Not sure why. I don't normally use it.