Problem read from MPS is solved incorrectly

(All files I refer to are attached [here](https://github.com/coin-or/pulp/files/7664137/files.zip))

I'm trying to solve the problem in **mkt.mps**. If I solve it using CBC on the command line, it takes about 2 minutes and it finds a solution with value -170 (see **cbc-output.txt**).

However, if I solve it using PuLP as in **example.py**, it terminates immediately and PuLP claims to have found a solution of value 0. See **pulp-output.txt**.

Could it be a problem with reading the MPS file? I found issue https://github.com/coin-or/pulp/issues/459, but I have no way of telling whether it's the same bug.

As you can see in the logs, PuLP is using CBC version 2.10.5, and on the command line I used 2.10.3. The PuLP version I'm using is 2.6.0.

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