According to the spec, "textStringJustification = 'center' adds equal padding chars left and right of the string contents if the string is too short... It adds one extra padding char on the left if needed."

I wrote an unparser test for this, and it seems that the unparser is actually adding the extra pad character to the right of the string instead of the left.

See test:
unparseDelimitedPaddedString05
in the following files:
daffodil-test/src/test/resources/edu/illinois/ncsa/daffodil/section13/text_number_props/TextNumberPropsUnparse.tdml
daffodil-test/src/test/scala/edu/illinois/ncsa/daffodil/section13/text_number_props/TestTextNumberPropsUnparse.scala
daffodil-test/src/test/scala-debug/edu/illinois/ncsa/daffodil/section13/text_number_props/TestTextNumberPropsUnparseDebug.scala