I have the unshakable habit of triple-clicking a paragraph to highlight it to serve as a mark of where I was at when i need to interrupt reading.
In the game you have to select units by dragging a box around them, and that habit has carried over to selecting text on the screen in pretty much every computer application.
I know that probably doesn't answer your question, but that would probably require a neuroscientist. It doesn't help me read personally, it just seems to be one of those repetitive tasks that slightly autistic people do.
Some of my coworkers share this habit as well, and they've never played RTS games, so it's acquired in different ways.
(1) not even on the claim that that bookmark has that effect.
No, clicking four times doesn't select the whole page.
It has to do with border-spacing between table cells -- when you select text that runs into the border-spacing, it resets the selection to go from 1) original cell 2) start of the table 3) next cell.
With more sane styling (ie: setting border-spacing to 0), the selection won't jump to the start of the table.
This is just heaven here: http://imgur.com/asQy8v3
Look at all those lovely lines and right angles.
I suspect it's related to some patterns when reading books, like putting a bookmark below your current line and moving it down, or following your current position with your finger.
I'm glad to hear I'm not the only one! I compulsively select random blocks of text: select up, select down, repeat. I definitely get annoyed with the popup-menu-on-select feature of Medium, but I feel I can hardly blame Medium for my random, compulsive habit.