Sometimes my ship just moves sideways without me pressing anykeys!

You probably have/had the capslock key pressed. Turn it off and try pressing strafe buttons a few times.

to expand on what grzy said:

vendetta treats capital and lowercase keypresses as different events. what will sometimes happen (particularly with the "a" key) is you will press the key to strafe, and accidentally bump the capslock key, turning it on. then, when you release the strafe key, it counts as a different key being "released" and will fail to recognize that the strafe key is no longer pressed.

(example press 'a' to strafe, accidentally catch the capslock key so when you let go of the strafe it sees that you released 'A')

the fastest workaround to this is to go into options/controls/keyboard and map both lowercase and uppercase letters to your strafes/rolls.

the same result can also occur if you accidentally press the shift key just as you release the strafe, once again causing it to see the uppercase released instead of the lowercase.

edit: it does not seem to do this for everyone, as I have only the lowercase keys bound on my machine, and i never have this problem.

thank you!