Debugging information. On ios 8 ipad in safari.
This is repeatable for me:
Select goban labels bottom-left in site settings and update site preferences. Open correspondence game in which it is my turn. Click on my opponent’s name. A stone is placed at A19 or somewhere near there. This is not the only way to provoke this error, but it is a repeatable way.
Select labels none. Same error.
Select labels “all sides”. There is no problem.
If I go back to “bottom left” again, the error returns.