Adding Users to Single Chest ChestShop Not Working

Minecraft Username:
Karin_88

Brief Description:
Adding a user via /cmodify @username or /cmodify username to a small/single chestshop is not granting them permission to access the chestshop. However, it works with double chests, according to @Unique_Beagle.

Instructions:
1. Make a chestshop with a single/small chest
2. Add a user via /cmodify @username or /cmodify username
3. The user should be able to access the chestshop but instead they're getting a message about not having permission to.

How many times did you recreate this?:
Quite a few times, with both non-staff (@billy_sastard777) and with another staff member (@DCxCyBeR)

Result:
The users are getting a message saying they do not have permission to access the chest.

Expected Result:
They should be able to access the chestshop to add stuff/take stuff out.