The properties applied locally to the content are not preserved and used for the new content when the user changes the paragraph indent.

Workaround: Keep the properties in a variable and apply them after executing the command:

StyleDefinition style;

private void RadRichTextBox_CommandExecuted(object sender, CommandExecutedEventArgs e)
{
    if (e.Command is IncrementParagraphLeftIndentCommand)
    {
        this.radRichTextBox.CurrentEditingStyle.CopyPropertiesFrom(style);
    }
}
        
private void RadRichTextBox_CommandExecuting(object sender, Telerik.Windows.Documents.RichTextBoxCommands.CommandExecutingEventArgs e)
{
    if (e.Command is IncrementParagraphLeftIndentCommand)
    {
        style = new StyleDefinition(this.radRichTextBox.CurrentEditingStyle);
    }
}