Stretch middle button time interval

[Nick <debuser@acrasis.net>]

The middle button of my mouse (actually a 3-button laptop trackpad)
seemed to stop working in X after my jessie to stretch upgrade. It no
longer pasted text nor opened a web page in a new tab.

I since realised that it does still work but requires a limited time
interval between pressing and releasing the button. With a quick jab
it works, but if the button is held down too long before release it
does not work. The interval seems to be less than about 0.5s.

Is there any way to change this time interval?

Thanks
-- 
Nick