Hey ytianlong-
The reset to default option appears to be working as you say it should (keep the same scale ratio) when the lock is engaged. I tried adding a cube directly to the level as well as setting the scale of a static mesh component and skeletal mesh component inside a blueprint. If you are seeing the scale ratio change when using reset to default, please let me know where you’re changing the scale value as this may be an isolated issue.
Cheers