Wrong circuit breaker used, was it dangerous?

A licensed electrician worked on my house and installed an Eaton CH240 40 amp two pole circuit breaker in my Square D Homeline panel. The inspector didn't see a problem with it, though, frankly, he wouldn't have even looked at the panel if I hadn't asked him to. I was curious about the breaker since I didn't know that Eaton made breakers for Square D panels. In looking on the Eaton website, I found that they recommend a CL240 for a Square D panel. The CH240 breaker installed by the electrician was recommended for an Eaton CH panel. Since I had a spare Homeline 40 amp 2 pole breaker, I replaced the CH240 with the Homeline breaker. On removing the CH240, I noticed that the plastic on the back had been broken away near the buss bar attachment point, presumably because the CH240 wouldn't fit otherwise. Is this something that is regularly done? Was it dangerous?