Hi Chris,
The price list that you see on the Item Master data is not actually "selected".
What I mean is, the Price List drop down, and the accompanying field with the price, are merely "For Your Information". In other words, when you select any price list, you will simply be shown the price of the item in that particular price list.
In yet other words, selecting a price list in the Item Master Data window will not have any impact on the system. It does not set any defaults or anything.
Regards,
Johan