Update: Sources now say a newer build has been compiled, build 10586.218 that will go out instead of 10586.212. Original article follows, just replace all .212 references with .218.
Microsoft is now testing another new Windows 10 Mobile cumulative update, after releasing build 10586.164 officially for older Windows Phone handsets handsets. This new cumulative update is currently being tested internally, and much like previous cumulative updates, brings a more bug fixes and performance enhancements.
WinBeta can confirm that the new cumulative update finally fixes a bug that involved closing an app that was launched from the Apps List. Currently, closing an app launched from the Apps List would cause the background to essentially un-dim itself, making it hard to read text when using a light background. This issue is fixed in the latest Redstone builds, and is now fixed in the upcoming patch for current branch users.
For those curious, this new patch brings the current branch build up to 10586.212. Of course, due to the nature of internal testing, build 10586.212 may not actually reach the public if a newer build is compiled sooner with more fixes, so we will have to see.
Microsoft is mainly focused on the upcoming Anniversary Update for Windows 10, which will be launching for Windows 10 Mobile users this summer alongside the desktop release. The Anniversary Update brings changes to Cortana, Notifications and Microsoft Edge. In the meantime however, current branch users can expect more cumulative updates that fix more bugs.