Currently if you apply a one month membership extension promotion to membership contributions in a revenue batch, the extension adds a month to the expiration rather than change the expiration to the last day of the following month.
This does not make sense--the expiration should always be the final day of a month. For example, if someone purchases a membership in mid-April and used a promotion for a one month membership extension, their new expiration date becomes May 30 because April only has 30 days. The expiration should be May 31. This appears to impact transactions with promotions added in batch, but does not appear to be an issue for online membership transactions (the extension goes to the last day of the following month).