Not seeing a change when an image that is scaled in the bin is dropped onto the timeline. Tested on square and 16:9 video with "keep A/R enabled."
Split-screen looks normal as well in the latest release. Experiment with the "Resizing Mode" options in the S/S dialog box...
No distortion noted, even if the images are scaled prior to using split-screen.
If you make a mistake immediately press <ctrl-Z> to go back, step-by-step. And Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, the AS choice is available by clicking the caret to the right of the Save Project button on the toolbar. That way you're protected, and shouldn't lose anything.