s3_key_format_tag_delimiters does not work

[NLP-BigDataLab]

I meet this problem that it seems s3_key_format_tag_delimiters does not work.
Here is my output:
[OUTPUT]
.....
bucket test
s3_key_format /$TAG[1]/tag=$TAG[2]/$UUID.gz
s3_key_format_tag_delimiters &

And the tag is "tag0&tag1&tag2"
But I find that in some case, the s3 key will be "/tag0&tag1&tag2[1]/tag=tag0&tag1&tag2[2]/xxx.gz", not "/tag1/tag=tag2/xxx.gz"
Does anyone else meet this problem?