Problem with modifying plain text record after conversion (AppleScript)

I have come across a problem when trying to modify the plain text content of a record after it has been converted.

Here is an illustrative script:

tell application id "DNtp"
	set theRecord to get record with uuid "[uuid]" -- markdown file containing "abcdefg"
	set convertedRecord to convert record theRecord to markdown in current group

	set plain text of theRecord to "x"
	-- result: plain text is "x"

	set plain text of convertedRecord to "x"
	-- result: plain text is "abcdefg"	

end tell

(The reason why I’m doing this is because convert consolidates transcluded markdown files into a single document.)

As you can see, the record created by the convert command refuses to modify its plain text field. Exactly the same thing seems to happen when using simple plain text (rather than markdown) files.

Is this a bug or am I missing something?

I’m seeing no issue here with the script as shown…

set u to "2EA3C60A-4642-4B4B-8AB8-C6676E457E4F"
tell application id "DNtp"
	set theRecord to get record with uuid u -- markdown file containing "abcdefg"
	set convertedRecord to convert record theRecord to markdown in current group
	
	set plain text of convertedRecord to "testing"
	-- result: plain text is "testing"	
	
end tell

Does this persist after quitting and relaunching DEVONthink?