I'm not very experienced with either of these modules, but, as ikegami points out, some of your code seems strange—for example, if you're going to put the result of decode_entries in another scalar anyway, why use the hard-to-read decode_entities(my $new = $old) rather than the more natural my $new = decode_entities $old? Have you looked at $decodedParsedContentWithDecodeEntities? I'd take a look at that, because, well, you have unexpected behaviour, and it's good to know what's happening every step of the way.

Also note that the Text::Sentence documentation says:

The split sentences function takes a scalar containing ascii text as an argument and returns an array of sentences that the text has been split into.

I'm also puzzled how you can get the gor : BLAH line at all. It seems that you're printing lines of the form word : words (why?), with the left-hand side a word in the right-hand side, but gor doesn't appear in the right-hand side of the output that you displayed.

UPDATE: For that matter, have you looked at $decodedParsedContent itself? A quick look at the non-XS part of the source for HTML::Entities reveals that it's just substituting decimal, then hexadecimal, then named entities. One can imagine a strange scenario where, say, the expansion of a hexadecimal entity creates a decimal entity; it's possible, though (I imagine) unlikely, that you're seeing that here.