WPF Changing ContentStringFormat does not change the shown text

_This issue has been moved from [a ticket on Developer Community](https://developercommunity.visualstudio.com/t/WPF-Changing-ContentStringFormat-does-no/1377350)._

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[severity:It's more difficult to complete my work]
Changing the ContentControl.ContentStringFormat does not seem to have any effect. Doesn't seem to matter if it is changed from code behind, using a binding or a trigger.

See the attached .net 5.0 project for an example. It doesn't work in older versions of .NET either like .NET 4.5.2.
[WpfApp6.zip] (https://aka.ms/dc/file?name=B6aebb6d3ea394c9a9f592fef8b98213e637519934029252446_WpfApp6.zip&tid=6aebb6d3ea394c9a9f592fef8b98213e637519934029252446)

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### Original Comments

#### Feedback Bot on 3/22/2021, 00:43 AM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

#### Feedback Bot on 7/5/2021, 11:35 PM:

I detected that this issue hasn’t received a lot of activity, votes, or comments in the past 90 days. Based on this, the issues severity and affected area, it’s my experience that this issue is unlikely to get fixed. To improve the situation, consider following best practices for quality problem reports, and giving us more details on how this issue is impacting you.

#### Johan Appelgren on 7/6/2021, 01:14 AM:

(private comment, text removed)

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### Original Solutions
(no solutions)