Seems a bit unlikely that half of the people with negative reviews changed their mind, the last and only patch didn't do much to fix the problems.
EDIT: also the positive reviews would have jumped a bunch if the reviewers switched, but they were at about 5k when I noticed negative reviews at 14k, and there're still under 6k positive reviews now with 8k negative. I suppose reviewers could have deleted the reviews themselves instead of switching, but again, seems much more likely WB got Valve to purge any negative reviews they could flag as no content or offensive which could easily be about 6k of them