Galio w interaction with DoT

just a question as to whether galio's w is supposed to heal off of EVERY tick of deathfire as playing against a galio with deathfire makes poke impossible because he would simply w and heal for every single time deathfire would damage him resulting in a brief, super potion that would restore him 300 ish health every bloody time...

would appreciate if a rioter confirmed as to whether this is an intended effect or whether this is a bug since it seems to imply that any DoT will also heal him in a similar manner..