Not sure if this is a bug or a feature but looking at the formatting of the code I'll assume it is a bug.

MDL-45031 removed line 63:
.tabtree li

But it left the lines above it:
.unlist,
.unlist li,
.inline-list,
.inline-list li,
.block .list,
.block .list li,
.sitetopic .section li.activity,
.course-content .section li.activity,
.sitetopic .section li.movehere,
.course-content .section li.movehere,

Which now inherit the line below:
.course-content .current

This messes up the theme, just wanted to check it was intentional?

Thanks,
Sky