The following bugs and issues are known for ksh 93u+m 1.0.9:

Memory leak when initialising associative array in subshell
https://github.com/ksh93/ksh/issues/94

command substitution botches output of non-waited-for child processes
https://github.com/ksh93/ksh/issues/124

typeset -L/-R: string length breaks on multibyte characters
https://github.com/ksh93/ksh/issues/189

Segfault with very large extended glob patterns
https://github.com/ksh93/ksh/issues/207

process substitution cannot be part of a larger argument
https://github.com/ksh93/ksh/issues/215

Builtins don't handle I/O errors
https://github.com/ksh93/ksh/issues/313

Associative arrays of various types fail to be unset
https://github.com/ksh93/ksh/issues/345

Variable with discipline function in subshell causes memory leak
https://github.com/ksh93/ksh/issues/404

Memory leak(s) when modifying PATH in various contexts
https://github.com/ksh93/ksh/issues/405

Discipline function .unset only called once for array subscripts
https://github.com/ksh93/ksh/issues/419

Function autoload apparently broken on DragonFly BSD
https://github.com/ksh93/ksh/issues/432

nameref fails with nested associative arrays
https://github.com/ksh93/ksh/issues/594

globstar fails to resolve symlink
https://github.com/ksh93/ksh/issues/629

Race condition in job notification
https://github.com/ksh93/ksh/issues/655

ksh remains in "noecho" mode forever
https://github.com/ksh93/ksh/issues/672

bogus typeset -p output for compounds with disciplines
https://github.com/ksh93/ksh/issues/729

test a = a b: undetected error bug 
https://github.com/ksh93/ksh/issues/739

Occasional "write error" when writing to pipe
https://github.com/ksh93/ksh/issues/741

sleep 10 | read hangs interactive shell after ^Z
https://github.com/ksh93/ksh/issues/750
