In the DWG Workmode, the text height override in a Dimension Style will be checked on after re-opening a file. If you uncheck the text height override in a dimension style and exit the file and re-open the file the text height override will be checked back on.
If the Text Style that the Dimension Style is using has a text height of zero the text height override will need to be used. Setting a height of a different value then zero and saving the style will then turn off the override.