This problem was mentioned multiple times on the forum, e.g.:
I’ve even asked @imac and @ikoshkin about it but I didn’t get reply about when are they going to fix it. I have opened ticket in helpdesk and also no luck there.
If someone is interested in fixing buy together addon, please write to helpdesk. They are prioritizing the tasks to implement based on the tickets received so the only way to have it done is by pressuring cs-cart team to acknowledge the problem.