Abreactions are quite common during somatic-based interventions. I have experienced them myself on numerous occasions, and have seen hundreds, if not thousands, of clients discuss memories and feelings that arise during the therapy.
One interesting aspect of Tai Chi and Zen Meditation, is that these apporoaches provide both an avenue to reveal and discharge repressed or forgotten schema, and at the same time offer a method for coping with it in a healthier way than was possible orignially when it was "encoded." Moreover, it is precisely BECAUSE of this method, that the abreaction occurs. That is, the more one can "let go" of manipulative/discriminiatory top-down attentional processes, the more that memories embedded with an emotional "charge" can be allowed to surface - and be discharged and examined more freely and clearly without recourse to "covering up" and "fleeing" the experience.
This is akin to therapy in general. If a person feels safe, they can discuss intimate thoughts and feelings, get a better perspective on them, and move on - freer for having done so.