Partial content duplicating from one site to another

Description

I have setup an English and Russian site in Craft. In some entries, I have a super table field with 2 redactor fields in it. These redactor fields are both set to 'Translate for each site', and the super table field has 'Manage blocks on a per-site basis' turned on.

I have noticed a strange issue though, where parts of the fields content is being duplicated from one site to the other.

For example, I created a new entry, edited and filled this field out with a few rows of content in the English version and saved the entry. I then went into the Russian version of the entry and added a few rows of russian content and saved. When I go back into the English version, the English content is still apparent, but some (not all) of the Russian blocks of content have been appended to the bottom of the field, as new rows of content.

When I delete the Russian content that has been appended, it doesn't have any affect on the Russian version of the page - so the same blocks are not deleted from the Russian page.

Posted the issue here too https://github.com/verbb/super-table/issues/318#issue-535777174 as I'm not sure if this is a Craft issue or Super Table issue...

Additional info

• Craft version: 3.3.4.1
• PHP version: 7.0.33
• Database driver & version: MySQL 5.6.45
• Plugins & versions: Super table 2.1.19

Reproduce the issue in Craft 3.3.4.1 with English and Russian sites, a Super Table field using per-site blocks, and translated redactor fields. Compare the saved blocks after editing each site, then determine whether the duplication belongs to Craft or Super Table; done means content remains isolated between sites.