This blog is updated daily.
A general description is here.
[g]regexpr(pattern, fixed = TRUE) returned match positions in bytes (not characters) in an MBCS locale if 'pattern' was a single byte.
[g]sub(fixed = TRUE) with a single-byte pattern could conceivably have matched part of a multibyte character in a non-UTF-8 MBCS.
findLineNum() and setBreakpoint() would sometimes fail if the specified file was not in the current directory.
[g]sub() could use excessive stack space when used with a very long vector
of non-ASCII data.