Create Accounting for Depreciiation is trying to post to prior period not the current open period

I posted mass addtions and ran depreciation in draft and create accounting.  The journal entry for Addtions posted in current period May-12, but the deprecation lines went to error as the Event Date was defaulting to 30-April-12.  My expecation was depreciation would post to 31-May-12 which is the open period for both GL and FA.  I won't be able to get GL open a prior periiod once was are in production so trying to understand why the deprecation event date looked to the prior month--it looks like these entries are now stuck and I won't know what will happen to deprecation expense until I close May and