Keyboard shortcuts sometimes not working

I use LingQ studying English on Google Chrome(latest) on OSX and Windows.
I don’t know when this problem happens.
But when I’m reading, This problems sometimes happens.
The only solving of this issue is to refresh the web page.
Is there anybody that have this problem?

I find this can happen when I hit two keys too quickly, for example if I select a hint for a word and then immediately hit a number to boost its status. I suspect that this triggers an uncaught exception in the Javascript that manages the interactions. It would be nice if this could be fixed.