Very interesting bag of magic, and baxter. I did a little research and you guys are right. This glitch only happens in the rockman 3 rom, but NOT the megaman 3 rom.
Here's proof:
when defeating hardman, or any boss, it'll run the code to setup the explosion stuff, all those little balls.
In the megaman 3 rom, there's this piece of code that specifically checks if your playing the hard man level or not, specified by $22, 03 is the hard man level.
So then it'll set the Vertical Camera register $FA to 00, to prevent the screen from being scrolled down a little bit if you beat him during his earthquake attack:
http://www.alienaa.com//members/1119/mm3rom.PNG
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But, in this same area on the rockman 3 rom, that code does not exist whatsoever.
http://www.alienaa.com//members/1119/rock3rom.PNG
The rock3 rom does have some differences cause alot of code banks are shifted to the left or right by a few bytes compared to the mm3 rom.
So then maybe there might be some more little glitches in the rock3 rom like this, which are fixed in the mm3 rom.
I found this out because im an expert with the inner workings of mm3 and know just about how anything works in the mm3 since i've been working on a rom hack of mm3 for years so far.
Interesting find though you guys. :) About this little glitch cause of the code not existent in rock3