[4.8] Windows on second monitor disappear


Scenario: Main window with level open on monitor 1, content browser open on monitor 2.
If I dbl-click on say a blueprint in the content browser on the second monitor it will open the BP as expected in the main window as another tab but will then hide the content browser (and an other windows) from the second monitor.

This is a basic example, I usually have several windows open on the second monitor but if ANY other tab on the first monitor is selected (other than the first tab) then all second monitor tabs disappear. If I re-select the first tab on monitor 1 (the main level editor) then the previously hidden windows/tabs on monitor 2 re-appear.

This behaviour is not present in 4.7.x but is in 4.8

Branch: 4.8 Source from Github (up to and including CL 2516789)

My OS is Windows 10, the two monitors are different resolutions, Monitor 1 = 1920x1200, Monitor 2 = 1920x1080

Running projects from the launcher or running debug via VS2013 (F5) produces same result.

I realise this is pre-release but thought you may not be ware of it, assuming it’s not just my setup.


More info, it seems that this behaviour only occurs when the parent window on the second monitor is the World Composition Window and not the Content Browser.

If the CB is the main window with WC window docked to it then all is well.

IF the WC is the main window with CB docked to it then it will hide when any child tab on the first monitor is selected.

Hey Fijit,

Thank you for taking the time to report this issue and I will respond back when I have tested what your are reporting and found any new or relevant information.

Thank you,

Hey Fijit,

Would you mind downloading the preview release and testing this issue again on your end? I would like to verify if it exists in the binary release for 4.8 preview 1.

Let me know what you discover if you manage to test this on the version requested.


Hi Andrew,
Yes the problem still exists in 4.8 Preview 1, on a new project.

Open Editor from launcher.

Create new project with default settings (except folder change in my case)

Create a “Maps” folder under “Content”

Create a new Level inside Maps folder, leave name as NewWorld.

Save level and enable World Composition on it.

Drop a cube in there and press Ctrl-S (Probably not necessary but I did it anyway)

Menu Window|Levels

This opens the Levels window floating on main monitor (usually).

Click the “Summon World Composition” button at the top of the Levels window.

Move the World Comp window you just opened to second monitor and maximise it.

Dock the “Levels” window into the World Comp window

Move the Content Browser from the Main window and dock it in the World Comp window on second monitor

Open Window|Developer Tools|Output Log

Dock Output Log as the second tab on the Main window, so it’s next to NewWorld tab.

If you now select the output log tab, the World Comp (and all it’s docked windows) will disappear from the second monitor.

Interesting note.
While testing I could not click on this reply (on the second monitor). It’s as thought the World Comp window was still there, blocking but fully transparent.
This also rings true as I cannot see any sign of a minimised child window attached to the editor.

Hope this helps.

Btw I’m on build 10074 of Windows 10 but the behaviour has been the same since 10049


Andy Coats

One more piece of useful info.

It seems that my second monitor has a display ID of 1 whereas my main monitor has a Display ID of 2 (I imagine that equates to 0 and 1 internally).

No matter which way around I plug them in, the driver always assigns the first ID to the second monitor (when both monitor are active).

Main monitor is DVI, second is HDMI (It’s an LED TV).

I’ll see if I can coax it into assigning them properly just to see if it makes a difference.

Hey Fijit,

A team member informed me that this issue is not actually a bug, and is working as intended by design. If any tabs are undocked from the main viewport and another tab is then docked to the main viewport it will hide any undocked tabs. This only appears to affect tabs that in the Menu > Window with exception of Project and Editor settings. This actually comes straight from the bug report that was created for the issue and what was considered as the final outcome.

This is by design, the window disappears as it’s part of the level editor.
It’s an unfortunate side effect the content browser is docked in that window.
We may make some changes in the future that could improve this, however they would be considered a larger task with a lot of work flows to be taken into account. This is currently all the information I have one this issue, and if you have any other questions or concerns feel free to ask.

Thank you,