Operating system: Microsoft Windows 10 Pro
Graphics card: NVidia GeForce GTX 970
Broken: 2.80 beta, 2018-12-28, a7c5f4f20657
Worked: I didn't have this problem with the latest stable release, 2.79b
Short description of error
While creating a simple add-on I came across this bug. 10-20% of the time when I run my script and try to use it, I get the issue. When changing the value of a slider in the window created in the bottom left of the 3D view by dragging with the cursor, the text editor cursor is moved back to the last position it made an edit, and backspaces are rapidly inserted at the end of the line that the cursor just moved to. Undo isn't aware of these changes, so you'd better remember what was just deleted or make frequent backups. Also, when it happens, the object added by the add-on gets added many times, instead of the slider just adjusting a value of the original object. Simply running the script again (after restoring anything that was deleted by the bug) will usually fix it.
Exact steps for others to reproduce the error
Based on the default startup. Try to make an add-on based on the "Addon Add Object" template, run the script either with the button or with Alt+P quite often, every time using your new addon to add your new object, and messing with the sliders. Within a few attempts you should have come across the bug.