Occasionally, double-clicking on a MathType equation after an eXtyles process has been run will open an entirely different equation for editing in Word 2007. The problem is related to the save to RTF that’s performed “under the hood” by eXtyles. In some cases (which have not been clearly defined to Inera), saving a Word document to RTF (even without eXtyles installed) will cause this problem with MathType equations when the RTF file is then closed and reopened. To avoid this behavior in Word 2007, run the MathType menu function Convert Equations on the Whole Document with the type set to Convert Equations to MathType equations. This should clean out or expose the underlying problem in the equation.
Note: This conversion does not work properly in some versions of MathType 5.x. Inera recommends MathType 6.9 or the most recent release, 7.4. Versions earlier than 6.5 and versions 7.x prior to 7.4 are not recommended.
This problem appears to be specific to Word 2007, and upgrading to Word 2010 may resolve the problem.
A tech note from Design Science (http://www.dessci.com/en/support/mathtype/tsn/tsn113.htm) provides information related to this issue.