Timeout question for exec type readiness probe

I have a question regarding the timeout in exec type readiness probe in kubernetes.
My kubernetes version 1.11
I have defined a readiness probe as stated below.

- /bin/sh
- -c
- sleep 600
initialDelaySeconds: 30
timeoutSeconds: 30
failureThreshold: 1

according to documentation timeoutSeconds parameter has no effect on the readiness probe for exec type probe. After the container start i logged into the container . What i found is that after every 2 min + the timeout value readiness probe timeout and kubernetes spin another readiness probe while the previous one is still running. when i execute ps command inside the container i see more than one sleep command running. each sleep command has start time of 2m + timeout value after the previous one.
Can someone explain what kubernetes doing with the probe in this case ?