Move up and move down content button

In /skins/demo/styleshhets/content/common.xsl, I added the calls to ametys-front-edition-move-content-button template with -1 and 1 offsets

1. I added 3 contents in the same zone in a page
2. In FO, I switched to edition mode for this page with a user with all rights
3. The up and down links are good. (I have contents 1,2,3)
4. On the content 1 I clicked on down (I have contents 2,1,3)
5. On the same content (1 in second position), I clicked on down (I have contents 2,3,1)
6. The content 3 (in second position, which was in 3rd position before) only has up button and not down

Note: production mode