'm'ail_to_someone with mime_forward off is buggy

'm'mail_to_someone with mime_forward=off (default) may cripple the included
message:

if the article is in ISO-8859-1, the locale is set to UTF-8 and outgoing
charset is ISO-8859-15 the outgoing message has the 8bit chars replaced
by ?.

without digging through the code, my guess is that we copie the article in
it's original charset (ISO-8859-1) into the letter, and later we read it in
with the assumption that it was already converted to the local charset
(UTF-8). when it's written out again the conversation local charset (UTF-8)
to network charset (ISO-8859-15) fails as the message contains illegal
'UTF-8' sequences (which is plain ISO-8859-1).

anyone willing to look into this?