Quoted-printable string not decoded

[Charles Jie]

I found mutt can not decode qp strings in Subject if there is space in it. Such like

    =?big5?Q?Re: =BCW=A5[=B1z=AA=BA=A6=AC=A4J?=

If I change ' ' to '=20', it works.

Does the spec. of qp not allow spaces?

thanks,
charlie