CKEditor overflows AgentTicketCompose when replying to tickets with wide images (Znuny 7.3.1)

[uffIT]

Hello,
we are experiencing a UI issue in Znuny 7.3.1 when replying to tickets that contain large images.

Scenario:
A ticket contains an embedded image that is wider than the ticket reading area.
When clicking Reply, the system opens the AgentTicketCompose screen.

Issue:
The CKEditor content area expands horizontally beyond the visible window width.
Neither the editor nor the browser window shows a horizontal scrollbar.
As a result, the “Save as draft” and “Send” buttons are pushed outside the visible area and cannot be reached.
This makes it impossible to reply to the ticket under normal conditions.

Workaround:
The only way to access the buttons is to reduce the browser zoom level until the UI fits again, which is not acceptable in daily use.

Expected behavior:
CKEditor should constrain its width to the compose container, or
Horizontal scrolling should be enabled when content exceeds the available space.

This seems to be triggered specifically by images wider than the compose layout included in the original ticket.
Has anyone else encountered this issue, or is there a known fix / configuration option for CKEditor in Znuny 7.3.x?
Thank you.