This might be critical if others can reproduce this. Here's what I'm seeing.
I edited my site slogan on my dev site, went to admin/config/development/configuration/export and exported it, then went to prod site and admin/config/development/configuration/import to import it. The synchronize page correctly showed system.site needing an import. I clicked the button to do so.
Now, it says that both block.block.bartik.breadcrumbs and block.block.seven.breadcrumbs (which are disabled blocks) need import, because their region has changed from -1 to '-1' (a string). Presumably, this is caused by.
So that's annoying, but when I go to import the values on the synchronize page, it says it imports them correctly, but the same two config values are back again, same change (-1 to '-1').
I'm stuck in an infinite loop. :(