exchanging emails between professors
Usually, one should not do this because it might have implication on your current position, especially if you are not selected afterwards. 

Especially in academia, people might know each other very well and in such cases one might be tempted to make a short phone call or talk at a conference. 

If you want to avoid this, you should explicitely mention, that you don't want that your current advisor will be contacted because [insert good reason here].