Hi Duncan,
I cannot say for sure. Generally, TestComplete works fine with dynamic controls, it can recognize and update their properties and methods (as you have mentioned). In fact, it's the first time I've faced such behavior.
I have only one assumption: it may be caused by the internal architecture of the tested Datapicker control. As we have no access to its source code, it is difficult to say whether the name of the month is dynamically changed or there is another approach used for this procedure.
