See https://github.com/igbinary/igbinary/blob/9cca1574d9ee0ac58378965982309ae05e5a26e8/tests/igbinary_040.phpt

Currently, igbinary will unserialize the data without problems if there are extra bytes. However, extra bytes likely indicate that the data is corrupt/malformed.

php > var_export(bin2hex(igbinary_serialize(true)));
'0000000205'
php > var_export(igbinary_unserialize("\x00\x00\x00\x02\x05"));                                                                                      
true
php > var_export(igbinary_unserialize("\x00\x00\x00\x02\x05\xf8"));
true

Expected result for the last command: false and emit notice (Or a valid value and emit notice, possibly depending on an ini setting)