As the title says, when Throw Mine is traited with Gadgeteer, both the Throw Mine tooltip and the actual damage output is reduced.
I tested this in Heart of the Mists on the group of golems. I throw the mine into a cluster of them, then manually detonate it. I didn’t test the damage in PvE, but the tooltip changes in Lion’s Arch just like it did in Heart of the Mists, so it’s likely bugged there too.
The Detonate tooltip window remains unchanged, regardless of Gadgeteer setting.
Level 80 Sylvari.