There are probably several bugs. As the product matures, this is where you will find a list of those bugs of which we are aware, but which we have elected to defer resolution to a future version of SurfaceInterval. This is just a fancy way of saying "yeah, we know about it, but have decided not to fix it yet".
If you should run across a bug/issue which is not listed here, please be so kind as to report it to support@dancethetide.com. Doing so will help us produce a better product. You can also email us with any feature requests you come up with. We are always looking for new ideas, and want to insure that we are providing a product that meets your needs.