When worlds are recreated, maps, item frames and paintings are still there (everything else is gone). The worlds that were recreated were made in

Minecraft 1.5.2
Minecraft 1.6.4
Minecraft 13w39b

Each was recreated in 13w39b. For all three, paintings and item frames were duplicated.

Strangely, this doesn't occur when copying from 1.6.4 to 1.6.4, or 1.5.2 to 1.6.4.

(Two with almost same background are from 13w39b to 13w39b, two with different background are from 1.6.4 to 13w39b, and the one over the ocean is 1.5.2 to 13w39b.)

The item frames and paintings are also duplicated in different dimensions at the same coordinates, in both the re-created world and the original. A separate bug report, marked as duplicate of this one, also states the same problem with maps.

However, this issue seems to have been fixed in 1.7.4.

How to reproduce:
01 Create a world; regular, superflat, large or amplified; in any version of Minecraft that has maps, paintings and item frames; in Survival or Creative; on 64- or 32-bit Windows or Mac OS X (on Linux?)
02 In any dimension, place some maps, paintings and/or item frames

03 Restart and change the version to any beta of 1.7 or 1.7.1
04 Go back in the world

05 Travel to a different dimension (e.g. the Nether and/or the End)
06 Go to the coordinates where you placed the maps/paintings/item frames in the first dimension
07 The maps/paintings/item frames are still there

08 Save and quit to title
09 Re-create world
10 Travel back to the coordinates where the maps/paintings/item frames were placed in the old world, in any dimension
11 Item frames, maps and paintings exist at those coordinates