SUMMARY
Selection mode interrupts when pressing Shift+PgDn.

Use case: Use mouse click and paging (Shift+PgDn) to select a large snippet of text.

STEPS TO REPRODUCE
1. Click LMB where I want my selection to start, hold it.
2. Press Shift+PgDn to scroll one page down.
3. Move mouse pointer (while holding LMB pressed) to the exact location where the user wants to the selection to end.

OBSERVED RESULT
The selection is finalized in the state it was in when Shift+PgDn was pressed.

EXPECTED RESULT
Moving the mouse pointer (while holding LMB pressed) should continue changing one of the current selection's boundaries.

SOFTWARE/OS VERSIONS
Operating System: gLinux Rodete
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.11.0
Qt Version: 6.7.2
Kernel Version: 6.12.20-1rodete1-amd64 (64-bit)
Graphics Platform: Wayland
Processors: 12 × Intel® Xeon® W-2135 CPU @ 3.70GHz
Memory: 62.4 GiB of RAM
Graphics Processor: Quadro P1000/PCIe/SSE2

ADDITIONAL INFORMATION
Workaround #1: Instead of using Shift+PgDn, move the mouse pointer below the window edge and wait for the log to scroll sufficiently. It's ~10x slower though (the exact difference factor may vary), compared to scrolling with Shift+PgDn.

Workaround #2: Export the whole log to a file, then edit that file to keep the desired part.