I have set up various tax rules to accomodate all the different Canadian provinces, and they seem to work great for anybody proceeding through the checkout process.

However, I notice that after an order has been created (no longer a shopping cart), if I add a product to the order, taxes are not updated properly. Taxes seem to be removed for items I take off the order, but they are not added for any new products. (Often we facilitate order updates for customers, so this is a common case...)

If I understand this post correctly, it sounds like the taxed amount is stored as part of the "price field".

I've attempted to set up a rule that cycles over the line items of an order (when order updated/saved) and "Calculate taxes for a line item". I'm not sure why, but it doesn't seem to update anything.
Any suggestions?