maxp010- that might be more related to the behaviour than touchscreen issues. On slower devices - and even newer ones without updated graphics drivers - there tends to be a 'bug' caused when a browser refreshes slowly, and seems to get 'stuck' on moving a particular direction. When you tap the control again, it should fix it.
Put a message in your game if you detect that they're having that issue.
Remember, it's a bug not a feature.