it's not a bug.
The photos we see on the screen can't always exactly match the ball position the software has calculated.
The ball position the software calculates determines where your ball is, not where on the photos we see on the screen the ball is shown. That WGT can get the photos we see on the screen and the calculated position of the ball as close as they do is quite an achievement in and of itself.
So sometimes ball position around the hole doesn't jibe with the result calculated by the software and what looks top be in the hole isn't.
In the same way we sometimes see our ball on the screen in the rough but the game has determined our ball is on the fairway. Or the other way around, ball looks to be on the fairway but the game has determined our ball is in the rough.