Perl only recognizes the first 4096 bytes as utf8 because only
the first block of text have the BOM. So he thinks that the first
block is utf8 (and it goes ok) but recognizes all the other blocks
as Unicode.
That cannot be. Perl does not use BOMs to determine encodings. If a
file is opened with :encoding(utf-8) as
utf::all does, the entire file is assumed to be in that encoding.
Here's something to try: get rid of any BOMs completely. In your
original code, add this after populating $text.
$text =~ s/\x{FEFF}//g;
See this old discussion:
UTF-8 text files with Byte Order Mark.
Also, make sure utf-8 encoding is correctly specified in your HTML header.