Looking more closely at the steps from the Steps Recorder. The user copied the text from a DevExpress RichEdit Control that is embedded in a DevExpress grid. I tried a few times to recreate the error, but I'm unable to. Also, the DevExpress RichEdit component uses the Windows RichEdit DLL, I have it set to use the 4.1 version. Also, all the rich edit fields in that section of the software uses a dialog that has TAdvRichEditor on it, in order to apply any formatting to the text. If they don't use the popup rich editor dialog, there is no formatting and just text.
I don't know if how long an application is running can make any difference(although it shouldn't), because the application was running for 4 hours and 40 minutes, when the error occurred.
But, as you said not knowing the RTF that is being pasted, it might be a little bit more difficult to fix.