The Nexus 4 (Mako) and Nexus 7 WIFI 2012 (Grouper) both come without the lockscreen transparency option enabled in the latest version of Android called Kit Kat. To "fix" this behaviour, head over to the Android Downloads
section and get the appropriate zip file. Flash through recovery or sideload with ADB.
Note: Use only on stock version of Android 4.4
Note2: The flashable zips are for build KRT16O only. Will update the download section with the newly build KRT16S zip later today.