I have found some bug signs. This time, it happens to appear depending on the order of your layers and not just the size of your image per layer.
The bug that has been said before was in this order in layers: Layer 1 has 1920x1080, and Layers 2 and 3 has 1920x1200. Disabling either Layer 2 or 3 do not make any difference in this case. Note that Layer 3 is the top layer.
However, making the Layer 1 as the top layer, then disabling 1 of the 2 1920x1200 layers seems to fix the problem, and renders exactly what is in the preview window before rendering. But in this case, I included a Transparency Effect so the background elements can be seen even if it was meant to be at the topmost layer.
Although when I leave the layers enabled, the bug is still present. Seems like one layer is being outnumbered by the others, and that makes the scaling-down of the other elements, which was the function of the Widescreen Fit.
I'm still experimenting with the bug. Will keep you guys updated with the findings.