Pressure plates stand out of the item frame

Actually this seems to be the case for all solid blocks.

... not only for solid blocks, even all blocks. Only items are flat.

Resolved as Works as Intended.

Not true. Flowers (non solid blocks) are flat, also Lava/Water (non solid, too) is flat, for example.

And "Work as Intended" ? Really? Item frames look like images to me. A image should be 2D all the time.

The stuff is put in the items frame with the exact same model as in your inventory.
(The rendering of the flowers and plants as block are not a solid block, it's two sprites standing crosswise.)

"The stuff is put in the items frame with the exact same model as in your inventory."
why do pressure plates and stuff like that look completely different in my inventory then?

There it is (left: Inventory, right: Frame).

Sorry, but the items in the inventory shown in a isometric view from above. If you look in the same angle onto the item frames, the items there are exactly the same.

As a general rule, non-placeable items render as they look in the inventory, while placeable blocks render as they would really look.

@Kumasasa Well, I see we have different views on this. So I started a discussion at the forums to stop wasting your time.

For reference: http://www.minecraftforum.net/topic/1584037-solid-blocks-on-item-frames-should-be-rendered-2d/

Ok. Good solution. You may of course link to this ticket here, if you like.