0.17.16 to be specific. I updated to 0.17.25 earlier today and am still seeing it. Yeah, with bob's mods magnifies the effect significantly. But as I mentioned in the post, I suspect that it has something to do with any time that a building speed's crafting speed is greater than 1.

I discovered this while playing modded Factorio (Bob's et al) where the effect of the bug gets laughable (I maxxed it out at creating 93 steel gears from a single steel plate even though the productivity modifier on the assembler was only 260%), but I believe that the bug exists in Vanilla as well. ...