Contraction validator does not pick up some common contractions

[edwardwoodward]

Testing this I noticed that the validator Contraction ignores some common contractions.
For example, it picks up don't, doesn't, won't, isn't.
But it does not pick up aren't, can't, wouldn't, couldn't, didn't.

Is this validator checking against a word list? If so, is there any way of adding these to the word list?

[edwardwoodward]

Update:
Just in case anyone's thinking of looking at this - testing this again, I put all of the following in a text file:
It doesn't matter.
I'm not sure.
You're not here.
That's not right.
There aren't many.
He's daft.
It's immaterial.
I can't see.
It couldn't happen.
He won't help.
They don't care.
It wasn't real.
They weren't helpful.
You'll be late.
He thought we'd fail.
I think she's had enough.
He wouldn't tell me.
You shouldn't do that.
There's nothing to see.
Let's try again.

Contraction flagged them all except "wasn't".