After further look into your project, we noticed that the culture does not fall back automatically to the current thread, because you have at some point set culture for this report through the Culture property. Then while playing around you probably decided to remove the culture, but instead of resetting the Culture property you've set it to (Default) from the DropDownList, which for some obscure reason serializes the following in the InitializeComponent method:
this.Culture = new System.Globalization.CultureInfo("");
After resetting the Culture property, this line is gone and the formatting works correctly without any further modifications in any of the supported platforms.
As for your inquiry, we do not notice such an observation, on our end. Changing only the CurrentUICulture only changes the UI and not other attributes which are in the domain of the CurrentCulture. You can see a short video with your project along with the revised project.
the Telerik team