The only issues I've had with buttonholes on my M50QDC have been with the weight of fabric causing the odd one to veer if I don't get the support right - usually alleviated by using the quilting extension table it came with.
Despite it being computerised, it's a mechanical one step buttonhole, using a lever to prompt it to change direction. I did mess one up, once, by nudging it with my finger but that was fixable with some hand stitching as the last leg just finished a little short.