Technically, a rollover would be Coverdell to Coverdell. A contribution to a 529 plan from money distributed from a Coverdell account of the same beneficiary is instead considered under IRC section 530(b)(2)(B) to be a qualified education expense that would make the distribution from the Coverdell account tax an penalty free if the contribution to the 529 plan is made in the same calendar year. The result is generally the same as it would be if it was considered to be a rollover, but there might be subtle differences in this case given the involvement of the excess contribution to the Coverdell account for 2015. In the case of a rollover, a distribution rolled over doesn't seem to correct the excess, while a Coverdell distribution used for a qualified education expense does.
