5. USB Mass Storage/UMS : There is a strange behaviour that seems to be related to the computers' USB chipset.
Depending on the PC I have tested it with (and even depending on the USB 2.0 or USB 3.0 port on a same laptop) once you have turned it off, you will have to unplug and plug the USB cable before turning it on again, otherwise partitions will not be mounted on the computer. Most of the time it does not show the second confirmation popup (which is not useful anyway, I think).
Finally, why does it say "Connected as an installer" in the notification area?
6. MTP file transfer fails with error message on Windows when transferring certain files (seems to be related to capital letters and/or unsupported file extensions). Still investigating...
7. Transfer all files through BT [including APK] does not work, neither in Explorer+ nor in CM FileManager. Explorer+ app developer claims that the issue is system related as his app simply calls available share options from the system.
Missing stuff that used to be there in previous releases
8. "Performance" is missing some options like "CPU voltage" and "Startup tweaks", Init.d, zipalign
9. BLN support missing (was already gone in 3.x)
10. FastCharge feature missing
11. Option to disable SlimBean boot animation
12. Battery icon styles "icon with text" and "icon with centered text" missing (they used to be available and still are in AOKP 4.2.1)
13. No navigation bar and nice background in CWM (like in some earlier releases
14. USB Mass Storage in CWM does not work
I hope these features will be back soon....
Missing stuff that would be nice
15. Add EAP-SIM WiFi authentification method (necessary for hotspots like "FreeWiFi_secure" or "SFR WiFi Mobile" in France)
This used to work in SlimBean 3.1 by replacing the wpa_supplicant file in \system\bin with a version taken from a 4.0.x Samsung ROM
However, in SlimBean 4.2.1 that procedure partly breaks WiFi support.
There are multiple references to EAP-SIM in "\system\bin\wpa_supplicant"
You might also want to have a look at here
Regarding AIO Dark Gapps
19. Default app selection window is still white. Is that the intended behaviour?
20. Could you replace SMS icon with a Holo Blue couloured one?