Maybe it was a case of Mr Sumner was not really supportive of...

Maybe it was a case of Mr Sumner was not really supportive of ABV going away from mining. When they have realised the interest in the "non-mining" brakes, they have realised that he wasn't their man.
Whilst the garbage truck brakes were right in terms of getting off the mining industry reliance, they appear to be the wrong product given lack of orders (come to think of it how are the truck trailer brakes going?). The Tera Dura brakes may well be the right product.
It could also be that whilst Mr Grey has been buying up shares, Mr Sumner hasn't not been. This difference in the confidence of the company's future may have also been a trigger?
And remember, Mr Sumner was taken off the board only two weeks ago..