At least, I think it's a bug. I ran into this while adding support for C++11 raw strings to cc-mode.

syntax-propertize-multiline seeks backward for the first position without a 'syntax-multiline text property, but searches forward for 'font-lock-multiline. For a span of text marked 'syntax-multiline, the new end returned from syntax-propertize-multiline will not be the end of the multiline text.

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