smsbox filtering on GSM 03.38 even when alt_charset is defined

Can anyone shed light on this?

In file sms.c function extract_msgdata_part_by_coding(), it filters on
the GSM 03.38 charset. This basically results in characters not in the
GSM charset to be replaced by "?".

But this happens with no consideration to the alt_charset config setting
in the "group = smsc". So, basically, if someone sets the alt_charset to
something other than GSM 03.38, none of the characters not in GSM 03.38
make it through.

Why is this? Is this not a problem?