Umbraco-CMS: Blocklist doesn't save on first attempt

I have blocklist setup in inline mode.

If I add a block and enter my content, it will not save, the postsave request contains an empty value:

{"id":2250,"alias":"leftColumnContent","value":""}

If I then refresh the page, and then carry out the exact same as above, it will save the content.

This happens on both v8.8.0 and v8.8.1

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This item has been added to our backlog AB#9258