Not for the first time in a personal comment or ask for clarification on one post.
Since it is directly related to the subject, I decided to post here the new edition. Hopefully, this time not so foggy out.

IMEI on our devices flies when you format and sometimes in piercing FlashTool-th.
To understand the nature of this phenomenon, it is necessary to plunge into the bowels of the EMMC. There's a section of / dev / nvram. It contains the IMEI, SN, MAC addresses of network interfaces, and others.
If you open a scatter it can be found in the 16-th row - __NODL_NVRAM 0xe00000. Start __NODL_ line makes fleshtul ignore this point. Why, in spite of this, it is sometimes rubs - I do not know. This is what is causing the disappearance of IMEI after flashing, and as is clear from the above, not only the IMEI. That is, we remove the section without giving anything in return!
So, / dev / nvram is flashed at the factory, and all further official updates and firmware even dare not touch it. No matter how the program part changes, it remains unchanged. In rare cases, the manufacturer makes changes to it, and releases firmware for service centers, including this section.

In working sitemy IMEI are on the path / data / nvram. More specifically / data / nvram / md / NVRAM / NVD_IMEI /. Directory / data / nvram created the first time the device starts up by copying it in the content / dev / nvram. Widespread recommendation to preserve the folder / data / nvram for repairing the keep in the future. It is certainly true, as the calls for backup, in principle. Calibration imeyami you can restore these, but this directory is useless at repairing the / dev / nvram.

What should be done in order to avoid problems in the future?
First you need to create a full dump of the device. I recommend to do it immediately after purchasing the product, prior to the search for a better world firmware. Depending on the dump method, among other files should be a file nvram.img. That img size of 5242880. This is the image of the desired section. Any nvram.tar and other ext4 is a copy of / data / nvram and no interest.
To create only the image of the / dev / nvram partition, you can use the command:
dd if = / dev / nvram of = / sdcard / nvram.img bs = 5242880 count = 1
5242880 is the partition size for devices on platforms 6577-6589. As a result, the path sdcard nvram.img file will be created. Store it in a safe place.

How to restore the erased partition / dev / nvram?
The easiest way to copy the previously saved file to the device’s memory is to type the following command:
dd if = / sdcard / nvram.img of = / dev / nvram
The result of the successful development of the command line will serve
10240 + 0 records in
10240 + 0 records out
5242880 bytes transfered in ... ..
For flashing this section FleshTulom find in skatere line __NODL_NVRAM .... and remove it __NODL_, then in the window select our nvram.img. It was chosen. Though he will be available in the program window, but FleshTul it did not pick up.
Sometimes fleshtul not want to sew this section separately. In this case, the firmware for fleshtula need to download, open the Management Board skater and noted, among other things, and nvram.img
In order to sew FleshTulom upgrate method, which requires the inclusion of all the items necessary only at the time of partitions, do the following:
Open scatter in any text editor. Appended to the beginning of the section lines that want to eliminate __NODL_. For example __NODL_PRELOADER 0x0. Save, open and scatter FleshTulom sew only those sections that were left uncommented, maybe FleshTul not see them.
This trick allows you to both hide and reveal items closed scatter. Thus, it is possible selectively to sew the necessary sections through upgrate, such nvram.

How to restore section, in the absence of a backup?
To do this, use a file from the donor. Ask someone in the subject line of your unit to lend you his nvram.img. How to get it written above. The disadvantage is obvious, we get the wrong IMEI, MAC, etc. Methods for changes nvram.img unknown to me, but there is software to edit the partition / dev / nvram (links below). After a successful amendment to the section, save his team as above.

SN Write Tool with drivers and manual
Maui META 3G
Video manual on Maui META

How do I know whether or not overwritten / dev / nvram?
Sense to check there, but if you ever "lost" the IMEI. It's enough to rekaveri reset the device to factory settings, thereby removing / data. If after the first run IMEI no again, then all that is written above - for you ..

A reasonable question arises - why all the Kama Sutra, where you can restore IMEI per minute using the software?
You can, but you "restore" it to the address / data / nvram, and "article" about how to restore an important section, which besides having a lot of the right and after mashing which marked problems of various kinds. Furthermore, it will fly off again at the next flashing.

Please note that the new version of the MTK Droid Tools received the backup feature / dev / nvram. Saved with the extension .bin

Methods tested and working. I restored three living unit and four offline. Last less than an hour ago koumiss.