Chrome Version       : 54.0.2840.98 (64-bit)
URLs (if applicable) : 
https://docs.google.com/spreadsheets/d/109_Dnoz1gnTLJ5JgH7xYom1qyPukHDSon1lfu3TWG38/edit#gid=0

OS version               : 10.11.4
Behavior in Safari (if applicable): Same
Behavior in Firefox (if applicable): Did not test

What steps will reproduce the problem?
(1) Open a new google sheets document.
(2) Select a cell using the mouse left-click.
(3) Hold command and click a different cell.
(4) Hold command and click the same cell as in step (3).

What is the expected result?
Clicking a currently selected cell, while holding down the command key, should deselect the cell. Visually this should remove the blue highlighting color on the cell.

What happens instead?
Clicking a currently selected cell, while holding down the command key, adds an additional layer of blue highlighting to the currently selected cell. The cell is not deselected.

For graphics-related bugs, please copy/paste the contents of the about:gpu
page at the end of this report.