When parsing an optional element, alignment that differs from following elements has been changed from a Schema Definition Error to a Schema Definition Warning. The spec needs to be updated to reflect this.
This is in section 12.1 Aligned Data:
"To avoid ambiguity when parsing, optional elements where the minimum number of occurrences is zero cannot have alignment properties different from the items that follow them. It is a schema definition error otherwise."
The requirement "DFDL-12-011R:alignment - avoid ambiguity when parsing" should be updated as well.