Please see the attached multi-output process in ILCD format. The allocation factors all sum to 1. However when you attempt to edit an allocation factor, even replacing a factor with the same number throws the error, "Not all allocation factors are summing to 1, please check you exchanges'.
I first noticed the problem with this process because if you create a product system with this process as a reference and run a quick results calculation, not inventory item appears for 'carbon dioxide, in air'.