Navigating to another frame or page is "when an element receives focus" and is at the same time a change of context. There is an anticipated change of context in navigation acts which cause an element to receive focus. [AT can track the focus.] What you want to eliminate is surprises -- context changes that could not be predicted from the prior context in which the focus change was precipitated. So you need language that distinguishes the surprises to be avoided from the context changes that the user will anticipate.
Proposed Change:
Re-state as (roughly) "When and element receives focus, it does not have any side effects in the form of a further change of context."
We have reworded the success criterion to eliminate any ambiguity that the receiving of focus is the change of context that is not permitted. The success criterion now reads:
"SC 3.2.1 When any component receives focus, it does not initiate a change of context."