No. not really.
I spent some time on the phone with Apple support and basically discovered that if I looked at the reoccurring event back in February (the previous month), it showed up correctly as an event being repeated as, in my case, "Custom, Every Month on the first Monday." However, then comparing that entry to the incorrect March entry, I noted the March entry was showing up as repeat "Every Month." (Which translated into every 30 or 31 days, looking at subsequent events.)
Simply changing the bad March event back to the Custom "Every Month on the First Monday," and then applying it to the forward "worked around" the issue.
We never did come up with any idea what caused the change. (i.e. the support person could find no references to any kind of similar problem.)
I was told to go to "www.apple.com/feedback" and to select "iCal" from the list of "OS C Apps" near the bottom of the page, and report the problem.
iCal on my notebook is fine but syncing my phone causes all the birthdays I have entered to be off by a day. You'd think both would be affected but apparently not. The more unfortunate part is I do all my changes on the notebook and just rely on the sync from there. From what I'm reading, I guess I have to edit them in my phone seperately. This is the same up-330-points-in-the-last-month-earning-us-billions-in-cash-reserves Apple company right? Ridiculous.