We realized that we have an urgent requirement to complete a series of automated testing stories in a sprint. Therefore we took in automation only stories. Some manual testers took in a few other urgent stories, therefore in the Doing column we have a bunch of stories waiting to be tested. 

Obviously this will continue going forward because there will be a backlog of stories to be tested, whereas development will continue (we can't halt development because of this).

Any suggestions to get around this issue? Throw in more testers? Btw, our developers (and management) don't think that developers are good testers because they don't have the tester's eye, so they're more likely to make mistakes in their testing.