OK, I purchased this product and took some time to run it through the fitting room like you have.

I'm having no problem with the fitting room product after completing the task.

Here are the steps I am using:

Create the mixed figure (in my case I dialed in the M4/K4 mix to 0.50)

Load the M4 Basicwear TShirt (do NOT attempt to conform)

Scale the shirt down to approximately 80% to get something resembling a fit

Go to the fitting room

Choose the TShirt as the object to be fit, The Mixed Figure as the Goal

Do not autogroup

Select the affected body parts (Neck, Shoulders, Chest, Abdomen, Arms, etc., etc. to the hip)

I transferred only one Morph - Body Morphs

Return to the Pose Room

Delete the original TShirt

Conform the now Fitted TShirt

Pose the figure.

Here is the result: