I would call this more of a 'round back lifting' than an imperfection.
The Kono movement is called a 'loosening deadlift' and is also seen in a few other places...Bill Starr recommends it somewhere, as does Dreschler in the WLE.
Another examples are doing hyperextensions with an exaggerated rounding and extension.
There are 2 schools of thought on this stuff.
1. Any rounding is bad, especially underload, and should be avoided.
2. Rounded back training, when done sensibly, can strengthen those small muscles and tissues that have to take the load when the spine rounds, so it's something to decide on a case to case basis.