[Nexus 7 Q&A, Help & Troubleshooting] GedBlake:
Hi, ReaperManHK...

I can't be 100% sure, because you don't explicitly state it in your post, but I suspect you've been using either

Flashify (for root users)

or

Flash Image GUI

.

Whichever app you've used, I'm pretty sure your bootloader is fine...(If it were otherwise, your Nexus 7 simply wouldn't boot... EVER! - it would be HARDBRICKED:().

Both apps (Flashify and Flash Image GUI) do essentially the same thing... which primarily is to provide an easy way of...

-------------------------------------------------

*** flashing a recovery.img to the recovery partition ***

...and/or...

*** flashing a boot.img to the boot partition ***

-------------------------------------------------

Neither Flashify or Flash Image GUI go anywhere near the bootloader itself.

NOTE: The boot partition is NOT THE SAME THING as the bootloader partition.

I suspect you've accidentally used either the Flashify app or the Flash Image GUI app to flash a

recovery.img to the boot partition:(

(and NOT to the bootloader partition... which I know is actually impossible using Flashify, and I also suspect to be equally impossible using Flash Image GUI).

It's not a difficult mistake to make... I know I've done it myself in the past (using Flashify to accidentally flash a recovery.img to the boot partition, instead of the recovery partition). This was easily fixed, by simply fastboot flashing a correct boot image to the boot partition.

Whilst generating your own device specific 'wheelie' blobs is a relatively straightforward task (though absolute care is required and the instructions MUST be followed to the letter), actually using them in the event of HARDBRICK/APX mode, seems to be less straightforward. The instructions on using them on the

flatline

web page seem a little ambiguous.

I strongly recommend YOU DO NOT run fastboot erase bootloader. This is a VERY HIGH RISK command, that may well permanently hardbrick your Nexus 7. If you must fastboot flash a bootloader, do it 'over' the top of the current one.. ie., without erasing the old one.

And, anyway...I honestly don't think you have a bootloader related problem:).

With regard to the strange 'glimpse' of the recovery on boot... this, I think, is quite common. I see it frequently myself... particularly if I've just been messing around in TWRP. I think the cause of the problem actually lies with the KitKat bootanimation (colored spinning circles) itself, as I never used it see with the Jellybean boot animation (pulsing luminescent X logo), that was for quite a while the stock Nexus 7 boot animation. The KitKat bootanimation starts ever-so slighty latter then the original boot animation, and consequently, it doesn't mask/hide the last screen you saw in TWRP. Anyway, whatever the precise cause, it has nothing to do with the bootloader:).

In conclusion...

Both Flashify & Flash Image GUI apps can flash two partitions, as follows...

a boot.img-->>boot partition

a recovery.img-->>recovery partition

What I suspect you inadvertently did...

a recovery.img-->>boot partition

(Overwriting the boot partition(kernel+ramdisk) and NOT THE BOOTLOADER partition)

Solution...

Use fastboot to flash a correct boot.img, with...

fastboot flash boot correct_boot.img

One final point... if you really had accidentally flashed a recovery.img to the bootloader partition, you would have wiped the bootloader itself, and which is absolutely critical to the Nexus 7... and your device would now be totally HARDBRICKED. An expensive paperweight:(.

There are no gradations of bootloader corruption... it either works, or it doesn't. And if it doesn't, well... :(:(:(:(:(... HARDBRICK!

So, If you're device is now running fine... as you seem to suggest it is... I wouldn't worry about it. I certainly wouldn't be inclined to start messing about with esoteric bootloader related stuff like 'blobs' and flatline.

A bootloader is something to be flashed as infrequently as possible... and then forgotten about... until and/or unless you really, really have unavoidable cause to do otherwise.

'boot.img to boot partition'

and

'recovery.img to recovery partition'

flashes, however, are relatively safe and innocuous... but just make sure you flash the right kind of .img file to it's appropriate partition.

Hope this helps.

Rgrds,

Ged.