Bulk Assign Tags with Filebird

I’m now using Filebird. When I try to bulk assign a tag to multiple media files within a Filebird folder, it misbehaves as follows:

1. If any of the attachments already have the tag, it removes the tag.
2. It sometimes removes -existing- tags and replaces them with -only- the one bulk assigned tag.
3. And on some attachments it may do -nothing-.

In short, it doesn’t seem reliable with Filebird.

What I want it to do is

1. If the tag already exists leave it alone.
2. If other tags exist for the attachment, leave them alone.

Can you help?