Asset container YAML file env variables changes when deleting images

Hi,

We have an S3 asset container which contains the following:

key: "{env:S3_KEY}"
secret: "{env:S3_SECRET}"
bucket: my-bucket
path: assets
region: eu-west-2
title: 'Amazon S3'
driver: s3
url: 'https://myurl.com/assets'
options:
  CacheControl: max-age=31536000

If I delete an image via the asset container GUI, the assets yaml file updates to:

key:
  env: S3_KEY
secret:
  env: S3_SECRET
bucket: my-bucket
path: assets
region: eu-west-2
title: 'Amazon S3'
driver: s3
url: 'https://myurl.com/assets'
options:
  CacheControl: max-age=31536000

And if I refresh my page I get the following error:

mb_strpos() expects parameter 1 to be string, array given

How come the asset container yaml file changes when I delete a file from the container?