With MP6 enabled and the WP_DEBUG flag set to true, when errors are produced, the left bar in the dashboard obscures/overlaps the error text.
In the normal dashboard theme, the left bar is pushed down to make room for the warnings and errors. Using MP6, the left bar does not "get out of the way."
I had some trouble reproducing this. I deactivated MP6, loaded up a dashboard page in a new tab, then went back to the first tab and reactivated MP6, and the left bar was making room for the warnings. I clicked around a few times, and it went back to getting in the way. Also, sometimes the bar will be out of the way for a moment after the page loads, then snap back up so it obscures the warning text.
It looks like in MP6, the left bar's CSS position is set to fixed, unlike in the default dashboard theme. Setting it to relative fixes the problem I've described, although I acknowledge that fixed has its benefits.
(Making the window less tall will eventually cause the left bar to snap down out of the way, FWIW.)