I've noticed on my 2012 Nexus 7 the actionbar has a horizontal line through it. This is not seen on my Nexus 4. Cropped screenshot. Line is just below text "Search for":
Ha that was a fun one to figure out. Turns out our action bar background image had a semi-transparent line at the bottom 2 pixels of it and since the file was in the incorrect application resources folder it was being scaled down on non-tablets and that bar was becoming impossible to spot.
I removed the weird line (I'm guessing it was from cutting out the assets) it from the image so all should be well after the 0.1.53 update coming out later tonight, thanks!