This patch fixes 2 quirks in smw:
-If you are holding left or right and going in that direction faster, would slow him down to his walking or running speed.
-Certain X speeds causes mario to unable to jump (despite playing the jump sfx), this happens when doing it on a boost block or being pushed very fast from an autoscroll.
Fixed issue with swimming. Mario was able to maintain his swimming speed after releasing carrying object.
This is because the deceleration code is horrible. When you press left or right, both the acceleration (go from an standstill to to moving) and deceleration (this is the capping of his maximum speed) applies which is why the value kinda shakes.
Also, in case if you are wondering, if you are fully running and let go dash while still holding left or right, mario will continue to run, and the dash timer ($13E4) will act like mario isn't running (decreases). Not a major issue though, you could possibly make it act as if the player didn't press left/right (without writing to $15-$18) by looking for a code at $00D687. Thank you for fixing it.
Also, did you use the latest version when updating it? I think I had two 2.0s while waiting. The very old one use an "ineffective" address on fixing this bug.
Considering he went to that specific submission and pressed the "submit update" button I'm pretty sure he knows that this is already in the section but modified it.
It's likely the bugfix he mentioned in some comment. However, since you didn't know about that he probably didn't ask the original author. It also looks like this doesn't include the readme for some reason...
Don't know why he didn't increase the version number though