Why esrollover max_size is not working

[winshenting]

esRollover:
enabled: true
conditions: '{"max_age": "1d", "max_size": "1gb"}'
readTTL: 168h
resources: {}
schedule: 55 23 * * *
options:
es:
create-index-templates: true
max-num-spans: 10000
max-span-age: 72h0m0s
timeout: 120s
index-prefix: qa
server-urls: >-
https://xxxxxxxxx
use-aliases: true
The configuration above is what I have wrote for configuring Jaeger.
It is strange that Max_Size is not working.
green open qa-jaeger-span-000001 0 50.4gb 25.2gb
as you can see, 25.2gb is over 1GB.
Can anyone give me an idea why Max_size is not working?
Thanks