Being i've mained Lucario for 2 years and know him to an almost scary degree, im VERY surprised that i never ran into it! Most likely because him being in the air is advantageous in almost all cases, since a 45 to 50 degree downwards approach with up-b is his best approach option, and it ALMOST ALWAYS starts aeiral combos. That of which are second to few in the game IMO. 45 degree up-b->dash attack->utilt->utilt->uair->uair->Fastfall->s-hop->u-air->up-b->u-air-> DEATH. OR 45 degree up-b->dash attack->utilt->utilt->uair->forcepalm->aurasphere. Aura sphere garunteed to hit a good portion of the time. Could also replace the dash attack in those with u-tilts. This is excluding ALOT of stuff, like fair and d-air as well for simplicity sake. Basically it's generally a good idea to jump as soon as you hit ground with up-b if you didn't connect, mainly because...well...SECRET. (okay okay it's because lucario pillars better then falco in melee) but thats a technique i won't be sharing huehuehue
ANYWAYS! TL;DR i never noticed the glitch because i always jump after hitting the ground if i don't connect. Thats not to say i don't chill out on the ground ALOT. it's just that during heated points in the battle, his best option is to be in the air thanks to those combos+pillaring+b-air is his best kill move+d-air is just shweet with its range+alot of characters have a REALLY hard time approaching in the air.
Hopefully i can fix that though...his actions are coded pretty funky for his up-b. Also, NEWB, i can't tell you for sure if it was coded that way intentionally or not since i wasn't around back then, but i can't think of any reason it would have been left that way. anyways, i leave of with THIS as a response to my own info-dump