Not possible to change attribute position values in 1.5.6

[patrmich]

Hi,

In Prestashop 1.5.6 > Catalogue > Attributes and Groups :
when clicking on the + button (more details), one can display the attribute list values.

Once displayed, it should possible to amend the value position (by clicking on the up or down arrow)

Unfortunately, when I do it, nothing happened.

Do you think that this problem could be in relation with the setting of max_input_vars (which is currently set to 1000).

Thank you in advance  for any reply.

Patrick