bg_fetch isn't working correctly

setting flush param: min_data_age 0
setting flush param: bg_fetch_delay 10
Connecting.
Flushing database.
Getting key (miss).
Getting value for ep_total_persisted.
ep_total_persisted: 0
Setting key using mc_bin_client.
someKey = 1
Sleeping 5 seconds.
Getting value for ep_total_persisted.
ep_total_persisted: 1
Getting key (hit).
Forcing an eviction.
Getting key (hit).
Unexpected info from get key (hit): END

Everything is working great until the last get - which is delayed for 10 seconds because of bg_fetch_delay. In another terminal, I'm telneting to 11211 and doing a mutation of someKey, but it's failing pretty spectacularly.

incr someKey 1
SERVER_ERROR proxy write to downstream
get someKey
VALUE someKey 0 1
1
END

So incr fails while a background fetch is going on, and the value is not modified.