Plural/singular verb?

[Chicken Sandwich]

We are employees of Quick Stop Convenience and RST video, respectively. As such, we have certain responsibilities which - though it may seem cruel and unusual - does include manning our posts until closing.

This is a bit of dialogue from the movie "Clerks". I find this sentence odd from a grammar point of view. How can "does" refer to responsibilities? Even though I'm not a native speaker, I'd say: As such, we have certain responsibilities which - though it may seem cruel and unusual - do include manning our posts until closing. (Since responsibilities is plural). So do instead of does makes more sence.
Can someone clear this up? I don't get it really...
Thanks.

 

[5jj]

You are correct. The verb should be do.

 

[SoothingDave]

"Clerks" is a funny movie -- but I wouldn't look to Jay and Silent Bob for grammar.

 

[Chicken Sandwich]

Well, it wasn't Jay or Silent Bob who said that, it was actually Dante.

 

[Tdol]

The plural subject is followed by it, which might account for the form used- the original subject has got lost behind the digression.