I can't remember the brands but when I was considering a shifter bracket and shifter or the mgw, I came across some posts about similar issues to yours. Some were defective and most were installed incorrectly. I'm not sure if that helps but good luck.

 

In the days before synchronized first gears I learned to "fake" a shift into second before moving the lever to first position. Just pulling toward second and feeling some resistance slowed or stopped the rotation and made shifts to first (and reverse) crunch-free. I still do it as a matter of habit, and it still works.