There are multiple tags and attributes in the Open XML model which define the formatting of the complex script characters and are not implemented in the WordsProcessing model. 

Such tags are:
szCs: Complex script font size;
bCs: Complex script bold;
iCs: Complex script italic;

Attributes:
cstheme: Complex Script Theme Font;

The cs (Complex Script Font) attribute is implemented in the export, but it is not preserved in the model on import.