#1: I fixed yesterday and haven't made a release with the fix yet.
#2: This is the Sonic 2 engine at work. Release the right button and voila, the spring works. I can't alter the engine, sorry.
#3: Look at a normal Sonic 2 ROM, and go to Emerald Hill 1. See that line at the bottom of the screen? It's an error that really has no fix. What I CAN do (and now will do) is move the bridge upwards a tiny bit.
#4: I kind of left this one, heh. It wasn't hurting anything :P. If it bugs you though, I'll add invisible solidity objects.
#5-1: Missed path swapper on my part, will fix.
EDIT: I take it back, it wasn't missed, it was misplaced. I mived it up a few pixels, should work now. You were in it but didn't pass through it because the box pushed you back up.
#5-2: Bad numbering on my part. The platform is marked as 18 03 (EHZ/ARZ falling) when it should be 18 00 (EHZ/ARZ stationary). As with #1, was corrected yesterday and will be in next release.
Before you mention it, I know that the corkscrew in EH1 doesn't work correctly if you run across it backwards. Also fixed and will be in next update.