Cancel executing query does not work most of the times. Whenever I try to stop execution of query that is rather heavy (thousands of entries to fetch or join of tables by un-indexed field) - canceling of the execution of such query never does what it suppose to do, it just hangs. You try to stop execution - you wait and wait - nothing, session hangs. Then you try to force disconnect to drop the session, it does not help either, whole application just hangs. And you end up force stopping it from the task manager.
This has been a long standing issue with Sybase/SAP that we are still working to resolve. We have fixed many of the cancel issues but if you still have some cases where you can send the sample SQL it would help greatly.