This scenario has been bothering me a long time but I could never figure out what I was doing to trigger it:

• press ctrl-g to zoom out, then zoom back in [this was the part I never paid attention to]
• now most keys stop working
• press ctrl-l [or really any ctrl chord]
• keys start working again

The drawback of overriding all handlers: you want to run some handlers. What I'd really like to do is give a name for every segment of handlers so I can explicitly say this then this then this.