Created attachment 155946 [details]
Screenshot of a resized KWrite text area

SUMMARY

In KWrite, one can grab invisible handles next to the window edges to resize the text area. I suspect this is inherited from Kate's panel resizing feature, just without the panels.

STEPS TO REPRODUCE
1. Open KWrite
2. Grab an invisible (with Breeze) handle close to a window edge or the border between the toolbar and the text area. For this, act as if you wanted to resize the window but grab the edge a little bit to the inside (the active area is large enough that this isn't very hard)
3. Move the handle to the inside of the window

OBSERVED RESULT

The text area gets resized, with empty content on the sides. See screenshot

EXPECTED RESULT

The invisible handles are disabled in KWrite mode/when there isn't any plugin.

SOFTWARE/OS VERSIONS
Operating System: KDE neon 5.26
KDE Plasma Version: 5.26.5
KDE Frameworks Version: 5.102.0
Qt Version: 5.15.8
Graphics Platform: X11