There is a difference in a Level 60 Ranger SoW and a level 60 Druid/Shaman SoW. I can never overwrite previous buffs despite casting as a level 60 Ranger. Nothing shows up on Lucy that indicates they should be any different.
http://lucy.allakhazam.com/spellhist...78&source=Live
Seems there was a bug report at one point relating to this aspect of SoW on items:
http://www.project1999.com/forums/sh...d.php?t=143990
[Sun Mar 08 22:47:40 2015] You begin casting Spirit of Wolf.
[Sun Mar 08 22:47:44 2015] Your spell did not take hold.
[Sun Mar 08 22:47:56 2015] You told Talsabis, 'you have one that i can't overwrite'
[Mon Mar 23 00:36:09 2015] You begin casting Spirit of Wolf.
[Mon Mar 23 00:36:14 2015] Your spell did not take hold.
[Mon Mar 23 00:36:18 2015] You told Svengha, 'remove current sow'
[Mon Mar 23 00:36:20 2015] You begin casting Spirit of Wolf.
[Mon Mar 23 00:36:25 2015] Your spell did not take hold.
[Mon Mar 23 00:36:26 2015] You told Svengha, 'for some reason i can't overwrite lol'