[R&D][FIX] Factory Mode / No lock screen / Power button issue

Affected models:

• Galaxy Tab 8.9" P7300 (confirmed by me)
• Galaxy Tab 7.7" P6810 (confirmed by sebi1964)
• Other Galaxy Tab series, including 10.1" (lot's of complaints on XDA, please confirm in this thread)

Symptoms:

• No lockscreen, regardless of the setting
• "Factory Mode" icon on homescreen, that opens up a calculator
• Power button powers off the device instantly: no menu appears
• No setup wizard after factory reset
• Open Lock icon at boot screen - maybe it's not a related issue (please confirm)

Myth:
Only Samsung repair center can fix it - FALSE!

Workaround:
Type *#7594# in the Factory Mode application and uncheck the box in the Shutdown App that appears after entering the code - Works in some cases, temporarily, till you restart

Fix:

• Rooted device
• Mounted /efs partition (if in recovery)
• Execute the following commands:
  
  Code:

  ---

  adb shell
su
echo -n ON > /efs/imei/keystr
chown 1001:1001 /efs/imei/keystr

  ---

• Reboot device
• Optionally: factory reset to get rid of the Factory Mode icon (or just delete it from homescreen)

Result:
All of the symptoms mentioned above are gone, except the lock icon at boot screen.

Needs investigation:
The lock at the boot screen may, or may not be related to the issue. It happens on my P7300, but to the following user's P7510 too: http://forum.xda-developers.com/show...64&postcount=1
What are the advantages of having a Galaxy Tab with unlocked bootloader? Or disavantages of having a locked one? How to relock?

Reference:
I've adopted Odia's solution for the Galaxy S3, spent some time with reverse engineering to see if it applies to our Tab's, if so, what are the differences, and voila! :)