R50f is a required security and bugfix release:

• Add a patch marker for vendor patch versioning to mksh.1
• SECURITY: make unset HISTFILE actually work
• Document some more issues with the current history code
• Remove some unused code
• RCSID-only sync with OpenBSD, for bogus and irrelevant changes
• Also disable field splitting for alias 'local= ypeset'
• Fix read -n-1 to not be identical to read -N-1
• Several fixes and improvements to lksh(1) and mksh(1) manpages
• More code (int → size_t), comment and testsuite fixes
• Make dot.mkshrc more robust (LP#1441853)
• Fix issues with IFS='' read, found by edualbus
• Fix integer overflows related to file descriptor parsing, found by Pawel Wylecial (LP#1440685); reduce memory usage for I/O redirs
• Document in the manpage how to set ±U according to the current locale settings via LANG/LC_* parameters (cf. Debian #782225)
• Some code cleanup and restructuring
• Handle number parsing and storing more carefully