The first thing I wonder looking at your video is what happened before the capture, because when the video starts the QCE windows is empty. Normally, it should contain the text editor control (Scintilla) or an image.
If it contains the text editor, it should show in the first section of the status bar the "Synced" or "Editing" status with number of characters.
And if it contains an image, it will show the status "Image" with its size.
In your case, it shows the status "Editing" (but the editor is not visible) and the number of characters is missing. Are you able to reproduce this situation? If yes, please tell me with what steps.
Second comment on your video: when you are in the editor, the "Find and replace" command (as every other commands under the "Command" menu) act on the content of the editor. Not on the Clipboard itself. Copying some text to the Clipboard and trying to execute a command produces an error if the text editor is not showing. I can probably detect the condition to replace the error message with a proper explanation "This command cannot be executed because...". But, again, it would help to understand how you got to this situation.
Thanks for your help.