Using pick block on an Item Frame with a signed Written Book/Book and Quill gives blank Written Book/Book and Quill

Confirmed. Same with Book and Quill.

This is suppose to happen.

Confirmed in 1.6, 1.7.4, and 14w02b. Effects any NBT, including item names, lores, and enchantments.

Crying Creeper

Crying Creeper

you can pick up the book, and then middle click it in your inventory...

You can't pick it up unless you knock it out of the frame. If you're in creative, you either have to destroy the frame's support block (which breaks any frames/paintings/buttons/levers/torches also attached to the block), or switch to survival to knock it out (and then switch back to creative to clone the book), otherwise you simply destroy the book if you left-click the frame. Also, that solution isn't really handy if there's no floor for the book (or you) to land on.

Anyways, confirmed in 1.7.5 and 14w10c.

Confirmed for 14w20a and b.

Confirmed for 14w31a. I experience the following:
Written Book and Quill in Item Frame: both Middle Mouse and [Ctrl]+Middle Mouse give you an empty Book and Quill
Signed Book in Item Frame: both Middle Mouse and [Ctrl]+Middle Mouse give you a signed book with the following text: "* Invalid book tag *"

There is no way to retrieve a written book from an item frame without destroying the block behind the frame.

Confirmed in the 1.8 pre-release. Even ctrl-pick block doesn't work. It will also pick block to any written book in your inventory. This also happens with enchanted items.