Nuke get(channels=0xf) but request(channels=0x7) error

I'm doing some paint fix work and Nuke is getting pretty annoying with its get(channels=0xf) but request(channels=0x7) error. It randomly throws it on different nodes and while in viewer everything renders correctly, Write nodes crash with an error.

At first I searched the forums and Nuke release notes but found nothing very useful except the discussion about motion vector channels in The Foundry Nuke user forum. First suggestion was to copy all nodes to clean project, but this didn't help me. Another suggestion was to remove motion vectors related stuff so I turned m-vectors off on all ScanlineRender nodes. It didn't solve the problem, so I started testing different things. After some fumbling I removed all other channels except RGBA from all pipes that come from renderers and it seems that this removed the error, at least for now!

So if you get these cryptic get(channels= ....) errors, try removing all channels that are not used, especially the motionvector channels, this might fix the problem.

A little teaser also: