In the image above the arms are low so the actual situation under the armpits is well hidden. 

Come, lassie, lift your arms high!

some fairing with the morphbrush (yes, that tickles!) shows the issue at hand: Ventilation hole.

this is because the collars are quite narrow, and facets were assigned to Upper_Arm_Bend. This of course would be avoided when the grouping were doen manually or at least fiting room would allow inspection and fixing of goups before creating a figure. 
The fitting room simply was not made to deal with 'A' posed figures. Maybe it works better with a more 'garment friendly' donor than the main figure.