honestly that does not happen, I created a new mix M4K4 in case it was a problem of my model.(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

Here I had to scale it again and place it on the model again

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

Do not autogroup

Select the affected body parts

I transferred only one Morph - Body Morphs  , I prove not transfer morph too , and tranfer all morph

Return to the Pose Room

hidden the original TShirt

Conform the now Fitted TShirt

Pose the figure and the result is disastrous as you can see, try a V4k4mix to test and the result is the same,I tried modifying parameters of all steps , copy joins , praying ,  burning candles and result is always the same honestly do not understand