Thanks for working/attempting to fix #1 I reported.
In testing .5.8 today, when disabling flymode, Minecraft has crashed to debugger info screen several times.
This seems to be half the time. I can't really figure out a pattern of what I'm doing when it happens other than I've pressed my fly key to disable.
See 2 attached logs. (Though, at least when it doesn't crash I land without any damage!)
FlyCrash.txt
FlyCrash2.txt