If your are flying in creative and you fly up and then hold down sneek, you will stop flying. (intentional)
Then if you let go of the jump button, intead of descending you will remain standing.
THEN, if you let go of sneek you will start continuously fly upwards (without pressing anything) untill you pause or open up your inventory.
1 Fly up
2 shift
3 let go of fly
4 let go of shift
5 you will be flying upwards without doing anything.
(may take one or 2 tries)
Related issues
duplicates
Comments

Cannot reproduce. Please force a crash by pressing F3 + C for 10 seconds while ingame and attach the crash report here.
Duplicate of MC-886.
How? If they were closed? I can take a video of it. Those aren't invalid.. It's duplicate if the past one is not fixed

Perhaps read a bit of the linked issue. That one was not closed because it had been fixed, but because the bug isn't in Minecraft (but in a third party library it uses). Thus "invalid".
There is no point in keeping such issues open that aren't part of Minecraft directly; keeping them open would just mean "hey, change something in Minecraft", and that won't help anything with this one.
MC-886? (see also e.g. MC-1341 (search is your friend)).