How about releasing everything when the ship jumps?
I have an alias that does +turbo, and I use the regular turbo button to turn it back off (press, release: it's off)

This is sometimes a pain as +turbo is still in effect, but the ship is not turboing, when I arrive in my destination sector after jumping.

How about having the client reset all keypresses when it comes out of myperspace, or as a part of "Loading..."?

Seconded.