When a healing draught is sustained by a perk (Healer’s Touch -trait, Ingenious Improvisation -passive), it is immediately consumed again. This results in double the usual healing (2x75hp). When this happens, healing share talents also proc twice, healing your allies for 40% of their max health.
However sometimes you receive double healing and the draught is also sustained. Given how rarely this occurs, I believe this happens when an item sustain perk procs twice in a row (the first proc giving double healing, the second proc sustaining the item). So if you have Healer’s Touch (1/4 chance of proccing), you would sustain your draught only 1 time out of 16.
Noticed this myself. Funny thing is this healer’s touch double heal bug can also impact teammates who don’t have it, if you’re playing with the heal share talent (3rd talent on the first row) and you drink a potion, if the healer touch sustain-bug occurs and you receive the double heal, your teammates will also be healed twice through the heal-share talent.
I think this healer’s touch bug has gone unnoticed for so long because a very small proportion of players actually run it, the vast majority go with natural bond, boon of shallya or barkskin.