I'm wondering why only chucks give such a strange bug. The SMWC RAM and ROM MAP tell us:
$7E:167A, 12 bytes, Sprites
Sprite properties, fourth Tweaker/MWR byte.
Format: dpmksPiS
d=Don't use default interaction with player
p=Gives power-up when eaten by Yoshi
m=Process interaction with player every frame
k=Can't be kicked like a shell
s=Don't change into a shell when stunned
P=Process while off screen
i=Invincible to star/cape/fire/bouncing bricks
S=Don't disable clipping when killed with star
and
3F6C7, $07:F4C7, 201 bytes, Sprite Misc.
Default values for $167A, various misc flags, for the standard sprites.
Change $07F57D (0x3F77D) from 00 to 01 to fix the glitched tiles that appear when a reflecting fireball goes into lava and make it display the normal lava splash.
It seems like chucks have a p flag so they give power-ups. And by memory watch (or something like that) we can list up which sprites give power-ups when eaten by yoshi I guess. I'm not familiar with hacking and have no idea how to do it. Hopefully someone will do.