Look at the TRV in his passport. It is a multiple-entry visa valid until 2016, right? However, this does not usually mean he can stay until 2016. Usually this type of visa means he can enter Canada however many times he wants (unless a number is specified on the visa), but can only stay in a Canada for a certain number of days for each visit.
For example, my husband had a 5-year multiple entry visa for Taiwan, but each time he came to Taiwan he could only stay for 2 months. So he would leave every two months, stay in Hong Kong or Macau for a few days, then reenter Taiwan.
Probably your husband is allowed to stay in Canada for 6 months each visit (though check - it should say this somewhere on the visa). So when he reentered Canada a month ago the clock should have been reset.
I think what happened is that the people processing the work permit did not look at his TRV, and told you he has to leave based on the refused work permit. Based on the still-valid TRV, he does not have to leave - provided the TRV is still valid.