"When you are processing a snippet of text starting with btex and ending with either etex or verbatimtex": According the MetaPost manual there are only "verbatimtex .. etex" blocks, but no "btex .. verbatimtex" blocks. "There is one special case: pens that are (possibly transformed) ellipses have an extra string-valued": In the current PDF, the "string-valued" gets hyphenated as "stringA" at the end of a line and "Bvalued" at the beginning of the following line.