Guild Wars 2

if you have two off-hand weapons equipped and only one mainhand, necro’s F1 Death Shroud and druid’s F5 Celestial Avatar won’t use the mainhand weapon when using the set without a mainhand while the other weapon set does, even though you can use it just fine outside of death shroud and celestial avatar

reproduce:
equip an off-hand in set 1 and 2
equip a main-hand in set 1 only
swap to set 2
look at your stats
enter death shroud or celestial avatar
watch stats go down

sigil and agony resist on the mainhand weapon also won’t function

https://www.reddit.com/r/Guildwars2/comments/4m4h8p

Same idea, with some screenshots documenting the impact on stats.