I believe there is either a hidden weighing for Rune of Havoc, or it doesn’t work on crafted axes.
I used about 15 Runes to try to hit a Tier 7 added Spell damage on several one handed swords. I made sure to even out the non tier 7 afixes before use. It moved, but never on to the crafted added spell damage.
So it’s one of 3 possibilities.
a) It doesn’t shuffle properly onto afixes that you craft on to the item,
b) There is some hidden weighing
c) I am unbelievably unlucky
I’ve had a similar issue where I’ve burned through about 30 RoH in the last couple of days trying to get a crafted Melee Void Damage on a 2H axe. If the tiers move at all (they often stay exactly where they are), they will bounce around the 3 other affixes. Occasionally the crafted affix will change, but not to the tier 7, and I came to the same conclusion as you, with their being either a bug or hidden weighting against the crafted affix… or I’m just completely defying the odds of a 1 in 4 event ~30 times in a row.
It’s made me want to stop playing, as the time and effort put in to get the Havocs is just extremely discouraging. According to developer Holly (in the Ziz and Raxx interview), havocs should be about as rare as ascendancy runes; why am I then able to get prophecies specifically for ascendancy runes, and NOT havocs? Ascendancy you only need to use once on an item (and then it’s either what you want or not), where Havocs you may need to use multiple on an item to get your desired result. I feel like this alone justifies creating a stand-alone Havoc prophecy, as i can already access prophecies that drop 12 ascendancy runes.
Do we know if this is a bug or not? If it is the sooner it’s confirmed the better. I myself blew through at least 20 Havocs trying to get the T7 moved onto a crafted mod with no success. Im less upset at bricking the exalteds (and have very few of the rare affixs left) but more about wasting the very rare Havoc runes.
Ascendency and Creation runes I can at least replenish via prophecies