I’ve been getting this weird glitch since plasma 6.3 update where any program that I open, that’s not fixed in the task manager, when closed leaves the space on the dock for a few seconds.
Hi! To help folks best guide you, could you please provide your basic system information from the Info Center app? The Copy Details button is the easiest way to get that ready to paste in:
Does the issue you’re seeing occur with the default panel setup?
SYSTEM INFO:
Operating System: Arch Linux
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.2
Kernel Version: 6.13.2-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 8 × AMD Ryzen 7 3750H with Radeon Vega Mobile Gfx
Memory: 15.1 GiB of RAM
Graphics Processor: AMD Radeon Vega 10 Graphics
Manufacturer: ASUSTeK COMPUTER INC.
Product Name: TUF Gaming FX505DT_FX505DT
System Version: 1.0
This effect only happens when I have the option “fill content” on the width parameter of the panel settings. With the default panel this behaviour doesn’t happen.
Hmm, what about theming? I see that you have a custom icon theme in use, but are there any other appearance modifications in use or installed - and if so, does the issue still happen with the default Breeze theming?
I am having this same issue. I will use a program that’s not in the dock, and when I exit, the space where that icon closed out will stay open for anywhere between 5 and 10 seconds, though sometimes it will close sooner if I hover over it.
I am using the default Breeze Plasma style. My information is below.
Operating System: Fedora Linux 41
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.11.0
Qt Version: 6.8.2
Kernel Version: 6.12.13-200.fc41.x86_64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5600 6-Core Processor
Memory: 62.7 GiB of RAM
Graphics Processor: AMD Radeon RX 7600
Manufacturer: ASUS
Ah - it looks like this issue has been reported through the KDE Bugtracking System: 499914 – Plasma panel doesn't shrink back when icon disappear
If you’d like to stay updated on that one, you can add yourself to the CC list in Bugzilla to get email notifications whenever new comments are added or the status is changed 
That CC list checkbox is located here - making sure that’s checked, then choosing “Save Changes” will add you:
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