You have this drawing...
You expected to see the Normal MText Editor window....
This happens because your Text Height is too small for the zoom factor. The MText editor automatically tries to adjust the size of the window to make the text readable.
To resolve this issue do the following:
- Start the Single Line Text command DTEXT.
- Click in any location
- Use the default values for everything except when prompted for the text height enter a number that is appropriate, in the example above 8".
- Enter some text and end the command
- Now place some MTEXT, it should be back to normal.
This has been verified to happen in AutoCAD and LT versions 2007 through 2009 and the workaround above works in the AutoCAD 2008 and 2009 versions but should also work in the other affected programs.
Autodesk has also published an article on this issue and you can view it here.