Mail: Keyboard multi-selection removes 2 items at a time when moving down

[s-aga-r]

Description

There is an issue with multiple selection via keyboard. When you shift-select and move up, it correctly adds to the selection, but pressing the down button removes 2 items at a time.

Steps to reproduce

1. Start a multi-selection using Shift + arrow keys.
2. Move up — items are added to the selection as expected.
3. Move down — 2 items are removed from the selection at a time instead of 1.

Expected behavior

Moving down during a keyboard multi-selection should shrink/adjust the selection by 1 item at a time, symmetric to moving up.

Reported by @rmehta.