When player taps a fetchland and the opponent has a Mana Flare in play, the fetchland ends up generating 1 colorless mana (besides the "fetch effect").

I assume this could possibly affect other lands that tap but do not generate mana.

Note: I haven't tested other combinations (AI using fetchland; player using Mana Flare), but at least it seems reproducible when AI has the Mana Flare and player uses fetchland.