This was reported by Geoff Clare in the comp.unix.shell newsgroup on November 3, 2011.

The bash man page says:

       -c string If the -c option is present,  then  commands  are  read  from
                 string.   If  there  are arguments after the string, they are
                 assigned to the positional parameters, starting with $0.

This is not actually how the option works.

It's an option with no argument, which causes the first non-option argument to be interpreted as a script, which can be seen if we add more options. (Consistent with POSIX.)

$ bash -c -x asdf
+ asdf
bash: asdf: command not found