A W, like stairs: front-left corner, left edge, back edge and back-right corner. The front-right corner's yellow faces right.
Algorithms
R U R' U R U' R' U' R' F R F'
12 moves
YOURS
Built from
R U R' + Sexy move + U' + Sledgehammer
Loose moves
R U R'
Trigger
Sexy move · backwards
U R U' R'
+ U'
Trigger
Sledgehammer
R' F R F'
Relations
Mirror
OLL 36
Your algorithm backwards
F R' F' R U R U R' U' R U' R'
solves OLL 31
That's why your scrambles are never the inverse of the algorithm: you'd be practising OLL 31 without knowing it. CubeDojo builds a random state with this case and checks it comes out.