Minor Lifesteal has been confirmed by the developers to now be considered as a skill's proc that won't proc other procs. This means that things like Minor Toughness, Spell Power Cure, Earthgore, Symphony of Blades and many other things will not proc off of Minor Lifesteal.
This is one of the biggest subtle changes to an element of combat in The Elder Scrolls Online that will surely affect PvE tank and PvE healer setups along with some things in PvP.
Unfortunately this change did not appear in the PTS Patch Notes nor the Markarth Live Patch Notes.