I'd say your problem is test coverage in the UI side of things. It sounds like you have the classic problem of one thing being changed intentionally affecting other unforeseen parts of the app. Just because there isn't Serious Business Logic in the front end doesn't mean it doesn't need to be tested.

If I were joining your project with the goal of attaining a sustainable and predictable pace, I would try and combine the front and back end teams into one team with ownership of the whole code base. If the response is "well, the front end guys aren't as strong developers as the back end guys" then perhaps you've found your answer as to why you're having regressions only in the front end. The answer isn't necessarily to fire the front end guys, but is more likely to be to shuffle everyone, and get the front end guys understanding what the back end guys do, and vice versa.

The first order of business would then be to get the front end tested as well as the backend. In my Ruby on Rails world, this would be Selenium for browser testing, Jasmine for javascript testing, Cucumber and Webrat for story level testing, and plain rspec for the controller and model level code. Don't be afraid to slow down and figure out what works for you - any code that's worth writing is worth test driving.