I was checking the blog module and basing part of what I'm building on the code of it, while I discovered this pretty nasty bug:
In the backend cms, the calendardatefield switches day and month, and so the calendar popup also gives the wrong date: today would be 12 februari instead of 2 december.
I can't imagine nobody has seen this yet? It might be possible it only does this in the last month?
I'll open a ticket for this....