Nasty bug in vertical scrollbar

[Bret Busby]

Hello.

In using UbuntuMATE 16.04.x, a nasty bug in the vertical scrollbars,
keeps causing problems.

When I am scrolling down in a web page, in a browser window tab,
sometimes, a menu listing the tabs in the window, appears. Sometimes,
it jumps to another tab in the window. It just now, jumped browsers,
and, opened the tab in which I was scrolling down, in a new tab, in
another browser.

How do I eliminate this nasty bug?

-- 
Bret Busby
Armadale
West Australia
..............

"So once you do know what the question actually is,
 you'll know what the answer means."
- Deep Thought,
 Chapter 28 of Book 1 of
 "The Hitchhiker's Guide to the Galaxy:
 A Trilogy In Four Parts",
 written by Douglas Adams,
 published by Pan Books, 1992

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