Weird player behavior

Hi there,

I am reaching out 'cause of this weird player behavior. We're in a middle of a production. We've decided for many reasons we would use custom navigation buttons. I am the integrator working with an e-learning specialist and a designer. Like many productions, I have to start with what I have in hands and try to make the most out of it. Now that all of the design has been approved, I am now switching from default navigation to custom buttons.

When I uncheck the default navigation, the player is rendering the slide leaving 2 white bands on each side. All slides, no exeption, that have the default navigation unchecked is affected.  I've attached a before and after pics. 

Slides have the same pixel size and the same aspect ratio.

I've noticed in the player setting the SLIDE section is not covering the entire display window. The SLIDE representation always stay with white bands on the sides whether or not slides are default or custom.

Must be a feature or something I don't know yet. It is been 2 years with SL2 and this is the first time this behavior pops out.

Help!