Not a bug in the closer sense but as it is now, the estimation for the Ortho Pixel Size in the Orthophoto menu is not really helpful since the value is the same unrealistic 0.00031 for both textured models (identical geometry), one with an unwrap of 0.01 and one with 0.001 texel size. The optimal texel size is 0.000967, so entirely unrelated.
Hello Gӧtz,
the optimal resolution for ortho-projection is calculated with respect to the several parameters, such as if the model is textured, the closest image detail, model quality etc. Therefore, it does not depend only on the texturing parameters. When using the optimal value, as much detail as possible should be preserved.
Hi Zuzana,
ok, but I’m sure there is no scenario where an orhtophoto with a pixel size of 0.0003 (three zeros !) is even close to reasonable with an unwrap of 0.01 (one zero !). In this case one texel of the unwrap ( with an ideal orthogonal view) would be rendered by more than 1000 pixels in the ortho ! ! ! Slightly overdone in my opinion. 
In addition, it does not change at all with different texel sizes. And the model quality is identical, as stated above, so no influence from that factor. Textured are all models, I thought that was obvious… 
All I’m saying is that the recommended Ortho Pixel Size has no practical use in this case. Generally, the optimal ortho pixel size should be the same or larger than the texel size of the unwrap.