Repro Steps:

1) Create a Project with a MainPage.xaml
2) Introduce a TextBlock to the Page
3) Clear the content of the TextBlock's 'Text' Property.
3) In the TextBlock's 'RichText' Property, type any sentence, then press [Enter] to confirm it.
Observe how only the "RichText" field is populated.

4) Save the Page, close and re-open it, and select the TextBlock again.
Observe how the 'Text' field mirrors the content in the RichText field.

5) Select the TextBlock's 'Text' field, and edit the text within it to whatever you want, pressing [Enter] to confirm it.
Observe how the text on-Stage reflects what was typed.
Observe how there is an asterisk in the Page's tab that indicates a change was made to the file.

6) Save the file, then close and re-open it.
Observe how the changes made, and seen in Step 5) are no longer present.

Expected Results:

Either:
a) [RECOMMENDED] The 'Text' and 'RichText' fields are always perfect mirrors of eachother. If any change is made to the RichText, is is immediately updated in the Text, and vice-versa. Meaning they will never get out-of-sync, and none of the issues above will be encountered.
b) The 'Text' Property and the 'RichText' Property are exclusive fields. Either by adding a dropdown/toggle, or by having a system in which the latest field edited wipes the other one, so that there is only content in "Text" or "RichText" one at a time.
c) The 'Text' Property simply doesn't mirror the 'RichText' Property, and we set an order of authority. So for example if a 'Text' Property has content, its given priority in rendering over the 'RichText' Property. The user would have to clear the 'Text' Property to see the RichText. This would however need to made clear to user, which may not be ideal in that it may require some sort of signal like an icon to show the 'master'.

Plus:

• The currently-active tab should never show an asterisk if a change has not been actually made to the file.
• The text on-Stage should never render content that actually isn't written to the XAML.