Skins are not compatible with the new file explorer with tabs. The tabs were sticking outside of the skin. Upon re-selecting default theme, the tabs are complete gone, as is the ribbon all together. This is unworkable.
This may or may not be a bug - but it definitely needs to be addressed either way. I've noticed that the font colors of the start menu aren't automatically adapting to their background to provide either white or black text. I have my entire taskbar and start menu set to transparent and the fonts are white in the start menu. This works wonderfully if the background behind the start menu is dark. But if it's white or a light color the text doesn't adapt and change automatically to black