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Window resizing when turning off/on external monitor in clamshell mode

silvetti

silvetti

macrumors 6502a
Original poster
Nov 24, 2011
952
376
Poland
Edit: I have renamed the thread to reflect more directly the issue, after a few steps of troubleshooting.


Hi!
I have this configuration:

LG 27UL850
  • USB-C - MacBook Pro 16
  • DP - HP Zbook 15u
The MacBook is being used in clamshell mode with resolution set to 2560x1440.
Display Settings

So lets imagine I am using my macbook I have my windows spread around with certain sizes.
Now I switch inputs on the monitor to my HP laptop, do some stuff there etc...
Then I switch back to my MacBook, my windows moved place and were resized to the bottom lower side of the screen.
It's as if when I switch inputs the laptop changes the resolution to something smaller which resizes my windows and when I switch back it does not revert the windows to their original sizes.

Anyone seeing this behavior? Or has similar configuration and does not have any issue?
Cheers!

Adding a before and after switching inputs example:
Before
After
 
Last edited:
This is the second time in a week or so I've seen a post about having a monitor connected to two different computers at the same time using different ports on the monitor. What does LG say about supporting this other than nothing in the manual?
 
BrianBaughn said:
What does LG say about supporting this other than nothing in the manual?
Click to expand...

I just did a test.
Disconnected the second laptop from the screen.
So just one laptop, one monitor.
I let the laptop go into sleep by itself after 10 minutes, monitor enters power down mode. Move mouse/keyboard everything comes back up correctly.
Then I just pressed the off button on the monitor, waited 5 seconds and pressed back on, all windows are messed up again.
So, not related to having two laptops connected.
 
silvetti said:
I just did a test.
Disconnected the second laptop from the screen.
So just one laptop, one monitor.
I let the laptop go into sleep by itself after 10 minutes, monitor enters power down mode. Move mouse/keyboard everything comes back up correctly.
Then I just pressed the off button on the monitor, waited 5 seconds and pressed back on, all windows are messed up again.
So, not related to having two laptops connected.
Click to expand...

Now you're troubleshooting! To clarify, which laptop and what cable were you testing there…MBP and USB-C?
 
BrianBaughn said:
Now you're troubleshooting! To clarify, which laptop and what cable were you testing there…MBP and USB-C?
Click to expand...

MBP and USB-C, yes.
Did another test, if I manually sleep the laptop but do NOTHING to the monitor (it still goes into it's monitor low power mode) and then wake up the laptop with external keyboard the windows behave correctly.

It's almost as if when I turn the monitor off, the laptop goes into a state where it sets a different resolution (lower one) (on the laptop screen, although I have it in clamshell mode).
 
For USB-C the manual states: "Features may not work properly depending on the connected device's specifications and the environment". That's not much help but it sounds like a catch-all.
 
BrianBaughn said:
For USB-C the manual states: "Features may not work properly depending on the connected device's specifications and the environment". That's not much help but it sounds like a catch-all.
Click to expand...

Wait, are you saying the problem is with the monitor? That somehow it reshuffles the window sizing and position?
 
BrianBaughn said:
The only way to know is to connect a different monitor via USB-C and test.
Click to expand...

I have now done a few more tests.
So, no issue with ZBook USB-C ->Monitor in "clamshell" mode.

I then thought of doing another test.

1st Test
  1. MacBook screen USB-C -> Monitor
  2. Macbook screen open, set to duplicate displays, optimized for LG 4K so I have same images in both screens and since resolution is optimized for LG if I look at the Mac screen everything is tiny.
  3. Turn off LG monitor, windows rearrange in "original best for Macbook resolution".
  4. Turn on LG monitor, windows reappear as they were before the screen being turned off.
  5. So correct behavior.
2nd Test
  1. Same as before but with one difference, clamshell mode, laptop screen closed.
  2. Turn off LG monitor
  3. Turn on LG monitor
  4. Windows positions/sizes are messed up

From all these tests I believe this is a macOS Catalina(?) issue.
Specially with the difference in results when testing with laptop screen open (mirror) and laptop screen closed (clamshell) causing different results.

Any opinions, or ideas?
 
Last edited:
I'd go with OS related. Using Big Sur here on a Mac mini and if my monitor goes to sleep, and I have to wake it my windows are all resized to and this is via HDMI.
 
And here we are in 2025 and it's started happening to me.
MBP M1 Max from 2021 on Sequoia 15.2 with a Dell U3818DW.
Just started today, if I put the laptop screen down, i.e. clamshell mode, the resolution on the Dell switches to 1280x720.
It's been working fine until today.
 
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