I can only reproduce this error WHEN the $body EOF declaration is missing, which is required for any custom island to work; if you restore your file and follow the guidelines within the file, as Ruben suggested (and as the system states to NOT change the lines) and it'll process the file properly.
Is your custom island coding following the example formatting, including the body eof lines?
The issue is that you've removed coding that clearly states not to remove (/* DO NOT CHANGE THE LINE BELOW */ and /* DO NOT CHANGE THE LINE ABOVE */; both of which being the EOF lines). As $body is a requirement for Custom Islands to parse, this is not a bug. A stock Custom Island generates coding as:
/* PHP CODE HERE, IF NECESSARY */
/* DO NOT CHANGE THE LINE BELOW */
$body = <<<EOF
Body of the custom box here
EOF;
/* DO NOT CHANGE THE LINE ABOVE */
