First off, Cleburne is natively 5-3-6 at all ranks. Hi might get the 7 defensive value from having gone up 1 EL (Experience Level - 1 star on his element detail panel) or he is a Corps Commander and got it form his Army Commander.
At any rate, if the former is true, he might lose some XP (eXperience Points) in being promoted, and therefore might revert to 5-3-6.
Other than that, Cleburne's abilities are:
* Gifted Commander, Entrencher
** Dispirited Leader, Entrencher
*** Dispirited Leader, Entrencher