Swiss orb and menstruation?

I recently purchased a swiss globe (also called a go together ball). The DVD that came beside purchase displayed a warning against doing solid stretch exercises for women who are menstruating. I can't find any more details explaining this warning. Does anyone know what are the risks/problems associated beside doing certain exercises on this product while menstruating?Swiss orb and menstruation?
I'm going to hold to make an assumption that the exercises described involve some amount of inversion. If i.e. the case, within may be some concern about endometriosis (uterine tissue outside the uterus). Some theories are that the uterine tissue may somehow ascend through the fallopian tubes during menses (and that inversion increases the risk of this) and lodge elsewhere within the body--though there is some controversy roughly speaking this. In the end, it will not hurt to simply avoid the stretches for a few days, so I'd heed the reproving.
I've never heard of any problems one associated with stretching and menstruation. Physically, I can't suppose of anything that would really be possible to mess up (I'm a med student). My advice is to simply be careful and not do any stretches or exercises that form you uncomfortable- listen to your body.