To the best of my knowledge, there has not been any case-law on the relation between the new EPO limitation procedure (Art. 105a and 105b EPC) and the nullity procedure.
The first decision in this regard has now been issued by the German Supreme Court (BGH, X ZR 72/08 "Kosmetisches Sonnenschutzmittel III).
There is a small catalogue of grounds for nullity of german patents, which is similar to the grounds for opposition in the EPC. Just as in the EPC, clarity does not count among these grounds.
However, if amendments are made during the nullity procedure in order to defend the patent in a limited form. the full examination including clarity is opened for theese amendments.
In the case at issue, the amendments were not made in the nullity procedure at the Federal German Patent Court (Bundespatentgericht) but in a co-pending limitation procedure before the EPO.
The BGH has now ruled that the claim as limited in the EPO-limitation procedure is to be considered as the valid patent claim and may not be examined for clarity because a pertinent ground for nullity is missing.