Soundcard buffer size affect mixdown time

When exporting a song in Cubase 8 i’ve noticed it takes a much longer time to export than from Cubase 7.5. After some fault finding i realised that changing my soundcard buffer size affects the audio mixdown time.

OSX 10.9.5
RME Fireface800 3.25drivers
Macbook Retina 2012 2.7ghz 16gb Ram 750GB SSD

Create a blank project
Drag in a wave file of reasonable length. 1-5minutes
Add some Steinberg plugins to add weight to the project. Any will do.
Then export audio mixdown 44.1khz wave 16bit realtime disabled

For me changing from 128samples to 1024samples decreased the export time by roughly 60%

Note increasing the buffer size will disable ASIO guard. I tried the same test at 128samples with ASIO guard off but this only had a tiny effect on export time.

Increased buffer. Changed mixdown location to a different physical disk.
Nothing changes… it’s just insanely and unbelievably SLOW!!!

There is already a feature request regarding adding additional buffers when doing non-realtime rendering.
Yes there is a big difference in rendering time depending on the buffer size, and it’s not a bug it’s just how things work. This btw also impacts render in place.

There is no logic to this behaviour. The Asiodriver and its buffer doesn’t play any roll during offline mixdown. I can make a Mixdown without any driver selected. The Asiodriver and its buffer is only in effect for all realtime audio wich comes from you interface or goes to your interface.
Changing Buffer shouldn’t have any effect on render time when its done offline.