Igor Pavlov - 2014-01-01

7-zip can open zip in zip.
But there is problem with htc zip archive.
It contains file firmware.zip
But firmware.zip is not good ZIP archive.
firmware.zip consists of some 256 bytes at start and then ZIP archive.
New 7-Zip doesn't want to open such ZIP.
But you can open it via menu Open -> ZIP or Open -> #.
Also you can open it, if you change extension of file: firmware.ttt.

Why 7-Zip doesn't want to open 256 bytes + zip as zip archive.
Imagine such situation:
You have 1 KB small.zip and 10 GB of another data in many files.
You archive all of these files to big.zip.
Then big.zip was corrupted by some reason.
And you call "Test archive" operation.
7-Zip can't open big.zip, but it can open small.zip inside big.zip.
It can show that it's OK with small.zip, but user wants to open and test big.zip.
So it's more safe to say that it can't open most expected archive - big.zip.