If a form control causes something to happen when a user tabs into it, this could be confusing for people with cognitive disabilities or people using assistive technologies, such as screen readers or screen magnifiers. If a new window must be opened, then users need to be made aware of what will happen before it occurs. This will allow the user to decide whether they want to leave the current window and it will also allow them to find their way back.
If a form control causes something to happen when a user tabs into it, make sure this is clearly indicated before the control. This can be as simple as a text instruction that says "Opens in new window" or "This will change the current language of the webpage". If the user will be unable to use the "back" button of their browser to return to the current webpage, make sure this is clearly explained.
No example is available.