Keys can sometimes get stuck if clicking while pressing a key (e.g. going forward then left clicking while going forward). This happened on 1.5.1 as well, but I also found it on the April Fools 2.0. I also noticed the actual Ubuntu cursor flickering...could be a bug.
Related issues
duplicates
Comments
migrated
migrated
Ahem. It was on 1.5.1, and the person in the post said "1.4" as the last version. 1.5.1 is different.
40th Duplicate of MC-886, please use the search function to see if your bug has already been submitted. Currently over 54% of tickets are being closed as duplicate.