This is a quite annoying bug which I was able to reproduce on another machine in a different project. It's related to the context menu that appears when you start typing in any XPath constraint. If you go down the list with your keyboard (up or down arrow) it sometimes thinks your input belongs to the main text box and not the context menu which will result in your caret jumping to another line. Same thing happens when you press Enter - sometimes, it thinks you pressed enter in the text box and not the context menu and it creates a newline instead. Steps to reproduce: 1. Insert a data grid anywhere on a page. 2. Select data source as Xpath, choose a random entity. 3. Begin typing your XPath constraint which should show the context menu with all the available functions, entities etc. 4. Go down the list using up or down arrows and observe how sometimes it doesn't register your presses in the context menu and instead tries to move your caret. If you're on Windows 10 it sounds an alert if you try to move your caret down one line when you only have one line in the xpath constraint box.
Have the same issue in 7.17.2. AFAIK I didn't encounter it while testing the 7.18.0 release.