Mmac
Smash Lord
Dang, too late for explanation of Bucket Cancelling
Oh well, I'll still explain:
When we look at similar stalls such as Marth's SideB, Fox's Shine, or Yoshi's Egg's, They're not really stalling, but rather just a momentum modifiers. All they do is just counter vertical Momentum with a slight boost (Or even a vertical stall), but they don't effect Horizontal Movement at all.
Now lets look at the Knockback properties on some of the Attacks, As you know, there's a property that the programmers they put in to counter Stall and Falls (Which is why moves like Toon Link's Dair and the such don't have the stalling properties when moved up). However the Momentum of attacks are still added to slow the vertical momentum which is why moves such as Toon Link's/Dedede's/G&W/Lucario/ect. Dair's still slow your momentum down.
I am not sure if this is a cause for some specials such as the Shine to have no effect on Counter Momentum because I think the properties return after an attack, but it might. Can someone test if after a high knockback attack on someone like Lucario, after he does a regular attack, does he get his regular Dair Properties back? Anyways what it looks like for now is that because there's no stalling properties in Fox's shine, the Vertical Momentum has nothing to stall his momentum boost from the shine, which is why he shines to his death.
Anyways, my theory is that because those 3 moves has no Momentum values on all the Axis's, the Knockback properties have no way to multiply with the Momentum values, therefore causing a complete stall no matter what situation. It's only my guess though. It also might be because they're "Free Control" moves (Where Momentum isn't factor in). It does explains Yoshi's Egg Roll/Spinning Kong, but unless G&W's Bucket does allow him to move slightly in the air, it is an oversight from the developers
If they were complete stalls though, then they wouldn't be effected the same by something similar like Diddy's UbB. I've even seen this on moves like Yoshi's DownB where his Stalling flip doesn't stall and he just moves graciously to the left until he lands.

Oh well, I'll still explain:
When we look at similar stalls such as Marth's SideB, Fox's Shine, or Yoshi's Egg's, They're not really stalling, but rather just a momentum modifiers. All they do is just counter vertical Momentum with a slight boost (Or even a vertical stall), but they don't effect Horizontal Movement at all.
Now lets look at the Knockback properties on some of the Attacks, As you know, there's a property that the programmers they put in to counter Stall and Falls (Which is why moves like Toon Link's Dair and the such don't have the stalling properties when moved up). However the Momentum of attacks are still added to slow the vertical momentum which is why moves such as Toon Link's/Dedede's/G&W/Lucario/ect. Dair's still slow your momentum down.
I am not sure if this is a cause for some specials such as the Shine to have no effect on Counter Momentum because I think the properties return after an attack, but it might. Can someone test if after a high knockback attack on someone like Lucario, after he does a regular attack, does he get his regular Dair Properties back? Anyways what it looks like for now is that because there's no stalling properties in Fox's shine, the Vertical Momentum has nothing to stall his momentum boost from the shine, which is why he shines to his death.
Anyways, my theory is that because those 3 moves has no Momentum values on all the Axis's, the Knockback properties have no way to multiply with the Momentum values, therefore causing a complete stall no matter what situation. It's only my guess though. It also might be because they're "Free Control" moves (Where Momentum isn't factor in). It does explains Yoshi's Egg Roll/Spinning Kong, but unless G&W's Bucket does allow him to move slightly in the air, it is an oversight from the developers
If they were complete stalls though, then they wouldn't be effected the same by something similar like Diddy's UbB. I've even seen this on moves like Yoshi's DownB where his Stalling flip doesn't stall and he just moves graciously to the left until he lands.