Account Management: Double scrollbar in long lists

Steps:

1. Go to Account Management
2. Click a client's name
3. In any tab (Users / Groups / Services) find a list that extends its boundaries (see attachments for examples)

Expected result:

There's an active scrollbar on the side of the list

Actual result:

There are two scrollbars on the right side of the list: one inactive and one active (see attachments)