Sucker Punch isn't programmed right

[Laiho1923]

ok, so on my sandstorm team i run a sucker punch cacturne, and i keep getting brelooms using mach punch against me. now in the game, sucker punch hits first, even when you use a priority move, but not in Shoddy--the priority move goes first and sucker punch fails. any idea when this is going to be fixed? i've lost countless battles because of this.

since everyone on Shoddy insists i'm wrong, here's some proof:

 

[Stellar]

If the user of Sucker Punch is faster than the opponent using a priority move, Sucker Punch will hit.
If the user of Sucker Punch is slower than the opponent using a priority move, Sucker Punch will fail.

It is programmed correctly.

This is illustrated in your .gif. Haunter is faster than Ariados using Shadow Sneak, so Sucker Punch hits.
In your case, Cacturne is slower than Breloom, so Sucker Punch fails.