Problem with GIF file scanner (flex)

The following flex code is supposed to scan a GIF file. A GIF file
begins with a Header and then a Logical Screen Descriptor. For some
unknown reason, flex will not enter the Logical_Screen_Descriptor
state. Also, am I right in using the character class [\x00-\xff] to
represent ANY 8bit char as found in a GIF file?


CODE...


byte [\x00-\xff]


%x Header Logical_Screen_Descriptor


%%
%{
    BEGIN Header;
%}
<Header>"GIF89a" {
    BEGIN Logical_Screen_Descriptor;
    printf("Lexer: Header: yytext is %s\n", yytext);
    printf("HEADER\n");
    return(HEADER);
}
<Logical_Screen_Descriptor>{byte} {
    unput(yytext[0]);
    read_logical_screen_descriptor();
    if(gif_ptr->gct_present) {
        BEGIN Global_Colour_Table;
    }
    else {
        BEGIN Data;
    }
    printf("LOGICAL_SCREEN_DESCRIPTOR\n");
    return(LOGICAL_SCREEN_DESCRIPTOR);
}


INPUT...


GIF89aHm blah blah lots of freaky characters blah.


OUTPUT...


--scanner backing up
--(end of buffer or a NUL)
--accepting rule at line 44 ("GIF89a")
Lexer: Header: yytext is GIF89a
HEADER
--scanner backing up
--(end of buffer or a NUL)
--scanner backing up
--(end of buffer or a NUL)
--scanner backing up
--(end of buffer or a NUL)
--scanner backing up
--(end of buffer or a NUL)
--accepting rule at line 56 ("H")
Lexer: Unrecognised header H
HEADER
parse error




Cheers,
Kristian.
[Hmmn. People don't often use flex for scanning non-text data, so you may
have tripped over a bug. -John]
--

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