Superior Rune of the same profession.
Not a bug pre-se, but more to do with that runes, (example ranger runes), you were not getting the full benefit from having only 1, even though it might have shown you were. Runes that are on your PVP armor also show on your PVE armor. Hence the 7/6, was before reading your runes on your PVP set as well. However, these do not count towards your PVE armor. You will need, in order to have the full effect again, have 6 Superior ranger runes.
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You weren’t getting the bonuses you thought you were — the display was glitched. In your example of Golemancer x5 + Ranger x1, you were getting the first five golemancer bonuses, but only the first Ranger bonus.
As Char notes, you were seeing the combination of PvP + PvE runes, which is why it said 7/6. Had you equipped six “of the Ranger” runes in PvE, you would have seen 12/6, but the bonuses would have been the same.
Apparently, this display glitch was fixed, so everything appears as it should.
That explains it perfectly! Thanks.