Currently, when in Play Mode and with a TextBox focused, pressing [Ctrl+A] to select all of the text within the TextBox also 'selects all' within the Studio UI (precisely; selects all Elements in the Navigator).

Furthermore, since the product UI and the Studio UI can be focused simultaneously through this method, deleting text content from a TextBox can also result in deleting Elements from the Navigator.

Video attached.

Repro Steps:

1) Create a Project with a MainPage.xaml
2) Introduce a TextBox Element to the Page.
3) Select the TextBox, and in its Properties, add a long string in the 'Text' field.

4) Play the Page.
5) With the Page still in Play Mode, click on the TextBox to 'focus' it (Focus can be tested by typing a couple characters after the TextBox has been clicked -- if the typed characters render, proceed to the next step)

6) With the TextBox still selected/focused, press [Ctrl+A] to select the entirety of the TextBox's text content.

Observe how all Elements in the Navigator have also been selected in addition to selecting all text within the TextBox.

7) Without deselecting/clicking off of either the TextBox's text or the Navigator Elements, press [Del].

Observe how all Navigator Elements are deleted from the Page in addition to deleting all content within the TextBox.

Expected Results: TextBoxes focused in PlayMode have exclusive focus versus the Studio Application's UI.