Thanks for your suggestions. You asked "How have you set your custom CSS class for the SpecialDays collection?". My sample declaration in the first post has "<ItemStyle CssClass="otherMonth_Web20" />". Is this what you are talking about?
I could try and use CSS to do a workaround, but it would seem that you have a major bug. Is there a way to escalate this issue to see if it is indeed a bug? I am under a tight deadline and need to decide quickly if I am going to try and use this control or something else.
The bottom line is that it seems that the css classes applied to a cell for any given special day should not vary from one month to the next. In other words, the second Sunday in April should always have the same css classes as the second Sunday in May. And May 24th should ALWAYS have the same css classes, and certainly should not change when you go back to April and then return to May.
If you try and reproduce this behavior using the sample declaration in my first post you will see what I mean. Have you tried my sample code?