New Outlook / OWA: Drag-and-drop email attachment fails when meeting is created from "Open in new window" Calendar

Hi,

I am posting this as a separate question because an answer on a related thread has already been accepted, but I have since identified a reproducible scenario that appears to narrow down the issue significantly.

Related thread: Unable to drag emails as an attachment to a new calendar invite item as an attachment (New Outlook) - Microsoft Q&A

In my testing, the problem is not that drag-and-drop email attachments are broken in general. The issue appears to occur only when a meeting is created from a Calendar window opened using "Open in new window".

Environment

• New Outlook for Windows
• Outlook on the Web (same behaviour observed)
• Multiple users tested

Working Scenario

1. Open New Outlook.
2. Create a new Meeting/Event from the primary Outlook window.
3. Drag an email from the Inbox into the meeting.
4. The email is successfully attached.

Also Works

1. Open New Outlook.
2. Drag an email directly onto the Calendar icon.
3. A calendar item is created successfully.

Failing Scenario

1. Open New Outlook.
2. Right-click the Calendar icon and select Open in new window.
3. In the newly opened Calendar window, create a new Meeting/Event.
4. Return to the main Outlook window containing the Inbox.
5. Attempt to drag an email from the Inbox into the meeting.
6. The email does not attach.
7. I can reproduce this consistently.

Additional Observation

The same behaviour occurs in Outlook on the Web when working with a separately opened Calendar window, which makes me wonder whether this is related to how Outlook isolates drag-and-drop operations between browser windows/processes rather than a desktop client-specific problem.

Question

Can Microsoft confirm whether this behaviour is:

By design, where Calendar windows opened via "Open in new window" are intentionally isolated from the main Outlook session and therefore do not support dragging emails from the primary window; or

A known defect/bug, given that drag-and-drop works correctly when the meeting is created from the primary Outlook window?

From a security and application architecture perspective, this behaviour appears somewhat logical if separately opened Calendar windows are intentionally isolated from the parent Outlook session. Preventing drag-and-drop operations between different Outlook windows or browser contexts could be an intentional boundary designed to reduce cross-window data transfer and help maintain session isolation.

If this is the case, it would be helpful for Microsoft to confirm whether this behaviour is an expected design limitation rather than a defect, and whether there is any official documentation describing how drag-and-drop functionality is intended to work between the primary Outlook window and Calendar windows opened via "Open in new window".

I would also be interested to hear whether other administrators or users can reproduce the same behaviour in both New Outlook and Outlook on the Web, and whether Microsoft has any documentation covering this specific scenario.

Current Workaround

Create the Meeting/Event directly from the primary Outlook window rather than from a Calendar window opened via "Open in new window". In this scenario, dragging emails into the meeting continues to work as expected.