In my last ranked game I played Thresh
and ranked my E first. I do not know if this played into the bug. The Relic Sheild 
( and Taragon's
) passive would not proc. It ended up proc'ing twice at one point midway through the game, but then went back to not working. Also the help technical section of PVP.net contains erroneous information about submitting reports through PVP.net preferences.
[slayer-jinx-unamused]
Hey Elarnia,
Thresh is classified as a Ranged champion, and only Melee basic attacks can proc Relic Shield's execute damage. Last hitting any other way will still give the heal/gold share though, and charging up his E passive helps with that.
Thresh is a ranged champion meaning IT DOESNT PROC
http://leagueoflegends.wikia.com/wiki/Relic_Shield
Melee autoattacks execute minions below 200 - 285 (based on level) health.
Killing a minion by any means heals you and the nearest allied champion for 20 health and grants them kill gold.
Read the bolded text above.
The EXECUTE is melee-ony and will not proc on ranged autoattacks. This means that you don't get the bonus damage to help you last hit the minion and must kill it normally.
The GOLD-SHARING and HEAL will trigger when you kill a minion through any source of damage (including abilities, Sunfire Cape, Thornmail, etc).
The tooltip is extremely clear and does not need to be 'fixed'.
