What you are going to want to do is submit a bug report against the calendar on Launchpad, a website pertaining to the development, maintenance, and contributions to Ubuntu software. This what you have to do:
- Make a launchpad account here.
- Find out exactly which package you have the issue with (when in doubt, submit the report against a more general package, such as unity, then someone can help you change it to the right one) .
- Make sure that the bug has not already been reported here.
- Submit the bug report, being sure to be clear and concise. A general layout to follow is to use 3 headings: "general issue", "what was expected", "what happened instead", "fix/solution/suggestion".
This list applies to any bug you wish to report.
Your contributions are always welcome and appreciated by the Ubuntu community.