I installed the Feb 18 CM11 nightly and quickly came across a problem with a service for one of the apps I wrote being killed, but never restarted.
Long story short, long-running background services (no notification) started with "START_STICKY" are not re-started after being killed in KitKat 4.4.2 like they were in other android versions. The fact that they are killed after some time (or after swiping away from the recent apps list) is normal, but failing to restart is not normal. If you go into Running Services, you can spot affected applications with at least 1 service running but with "0 processes".
This breaks a lot of apps, including widgets that update based on information from a service. Facebook messenger's process is even killed after some time, and notifications no longer come in.
The behavior is fine on 4.4 but is like I describe on 4.4.2 and coincidentally the newest builds of CM11.
Here's the bug someone posted on google:
There hasn't been any official response from Google, so no one seems to know if this is an intentional change.