Airmines should have been set for 45° bounce - the only reason they weren't I guess is they were a clone of some mine values - and mines use traditional behaviour.
--- a/hedgewars/uGearsList.pas Thu Apr 26 00:21:03 2018 +0200
+++ b/hedgewars/uGearsList.pas Sun Apr 29 09:24:14 2018 -0400
@@ -434,6 +434,7 @@
end
end;
gtAirMine: begin
+ gear^.AdvBounce:= 1;
gear^.ImpactSound:= sndAirMineImpact;
gear^.nImpactSounds:= 1;
gear^.Health:= 30;