assignments preceding special builtins persist as exported
$ yash -c 'v=foo :; env | grep ^v='
The assignment should persist as : is a special builtin, but I don't think it should be exported.
Forgot to log in again. I am the reporter.
The current behavior is explicitly allowed in the POSIX standard.
If the command name is a special built-in utility, variable assignments shall affect the current execution environment. Unless the set -a option is on (see set), it is unspecified:
(1) Whether or not the variables gain the export attribute during the execution of the special built-in utility
(2) Whether or not export attributes gained as a result of the variable assignments persist after the completion of the special built-in utility
It is surprising to me, though, that many other shells behave differently than yash.