XhtmlString content disappearing

Description

Steps to reproduce:

1. Open Chrome and run the Dev Tools by pressing F12.
2. Click the 3 dots and select Settings.
3. Click Throttling and click Add custom profile.
4. Enter a name for the profile, enter 100 in Latency field and click Add.

5. Close the settings and browse to the network tab in dev tools.
6. Select the profile you just created and keep the developer tools open and refresh the page.

8. Create a new page that contains an XhtmlString property using PropertyFor or EditAttributes in the View. (For example, the Standard Page on the Episerver Alloy site)
9. Single click the XhtmlString area to initialise the TInyMCE widget and add some content into that area then focus out to auto save.
10. Reload the page so that the widget has not been initialised.
11. Double click the XhtmlString area. The TinyMCE widget throws a javascript error and the content that existed in the property has now been removed.(Please click as fast you can before the page load is done.)

Expected:
The previous value is shown.

Actual:
The previous value is not shown. Sometimes, it's cleared out and saved.