Created attachment 184094 [details]
Video showing the bug, as well as showing that closing a program forces the task manager to refresh and group the windows.

SUMMARY

The task manager is not grouping LibreOffice applications together instantly when one opens files in the same LibreOffice application if they were opened via the Open option (File -> Open, or CTRL + O), creating two ungrouped icons of the same type of LibreOffice window on the taskbar; for example, 2 windows/icons of the process libreoffice-calc are displayed, instead of having both windows grouped under the same icon. It appears that opening the second file in LibreOffice doesn't cause the taskbar to refresh as expected. One needs to force the task manager to refresh to get the windows in the task manager to group together, which can be done by opening or closing another unrelated app or opening the task manager settings (among other ways). This bug affects both the Icons-Only and Icons-and-Text Task Managers on Wayland only.

STEPS TO REPRODUCE

1. Ensure one's taskbar is using the Icons-Only Task Manager. Ensure that grouping is enabled (Under Behavior -> Group, select "by program name").
2. Open a new LibreOffice Calc window in a Wayland session from either the Applications menu or a pinned icon on the taskbar. 
3. Open any file that opens in Calc (via CTRL + O or File -> Open). Note that the file must not be blank inside.
4. Using LibreOffice's "Open" option (CTRL + O or File -> Open), open a second, different file that opens in LibreOffice Calc. Note that the file must not be blank inside.

OBSERVED RESULT

The 2 LibreOffice Calc processes on the taskbar are ungrouped until one forces the task manager to refresh with another action.

EXPECTED RESULT

The 2 LibreOffice Calc processes on the taskbar should be grouped together immediately after the second file is opened.

SOFTWARE/OS VERSIONS

Operating System: Debian GNU/Linux 13
KDE Plasma Version: 6.3.6
KDE Frameworks Version: 6.13.0
Qt Version: 6.8.2
Kernel Version: 6.12.41+deb13-amd64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × AMD Ryzen 5 5560U with Radeon Graphics
Memory: 16 GiB of RAM (12.6 GiB usable)
Graphics Processor: AMD Radeon Graphics
Manufacturer: AZW
Product Name: SER

LibreOffice Version: 25.2.5.2 (X86_64) / LibreOffice Community
Build ID: 03d19516eb2e1dd5d4ccd751a0d6f35f35e08022
CPU threads: 12; OS: Linux 6.12; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Flatpak
Calc: threaded

ADDITIONAL INFORMATION

Calc was used for demonstration purposes, but the same bug affects the other LibreOffice programs (Writer, etc).

My guess is this bug is happening because LibreOffice opens an soffice.bin process of some type when a document is opened via CTRL + O that turns into the type of process being used (example: if using a calc file, it opens as soffice.bin which quickly turns into a libreoffice-calc window). The task manager may be refreshing too quickly to realize that there are now two active libreoffice-calc windows open; it's only looking at the initial soffice.bin process and separating it on the task manager, but doesn't realize that the process renamed itself afterwards and should now be combined until a refresh tells it to do so.

Opening the second file in step 4 via a file manager (Dolphin, etc) also causes the bug.

One can work around this in step 4 above by opening a brand new document (CTRL+N/File -> New -> Spreadsheet) instead of an existing document and then opening the desired document as normal in that new window (I believe this works because it skips running the file as an soffice.bin process first and goes directly to being a libreoffice-calc process). One can also work around this by opening or closing any other app or going into the task manager's settings, which seems to force a refresh of the task manager and makes the icons group together.

I've tried both the Flatpak and native versions of LibreOffice; the same bug happens with both.