achievement command works unreliable with statistics

The command /achievement works for statistics and achievements. It might make sense for achievements, but doesn't for statistics as it acts this way:

• /achievement give stat.leaveGame: increases the stat by 1
• /achievement take stat.leaveGame: reset the stat completely

This way the command has no real use.
And it also doesn't update the statistics then immediately (see also MC-55775), which seems to be a general statistics problem.