For what it's worth I have also had this happen many times over many versions of PSPad and I have observed that it happens most frequently after opening and closing many files, switching back and forth between projects etc. It seems to be a buffer overflow kind of issue where data gets randomly written to the wrong place.
I've even had it corrupt my project file to the point I had to manually rebuild it. I often have many files open so it takes a couple rows of tabs to show them all, and will run a test of the program I'm working on, open the compiler output in a new tab to review, close that, make changes and repeat. Or sometimes after doing search and replace across all files in the project so it opens and closes a bunch of files, or searching for a pattern, open the results in another tab then do another search to refine the results, etc. The common thread for me always seems to be opening and closing a lot of files. Possibly related is that as many files are opened and closed, and the number of tabs changes from fitting on one row, to needing two rows of tabs (or back again) PSPad loses track of which tab is highlighted, so when I look at the tabs it shows one tab highlighted, but the tab actually being displayed is a different one. I've gotten into the habit of just closing PSPad every so often when I'm opening and closing lots of files. The vast majority of my work is editing HTML, XML, and javascript, but lately (the past 8 months or so) I have mostly been developing in Python, but I'm developing code that produces XML files. Steve -- <https://forum.pspad.com/read.php?2,75694,76012> PSPad freeware editor https://www.pspad.com