When inserting keys in the viewport by pressing `I`, certain custom properties would not get keyed if their name was identical to existing properties (for example `scale`). That was because we use the name of the property to resolve an rna path and check if the path resolved. This was of course true in the described case and the square brackets would never be added. The solution is to check for `RNA_property_is_runtime` which is false for properties defined inside Blender. Pull Request: https://projects.blender.org/blender/blender/pulls/135304