When creating a new presentation slide shape, setting the alignment to something other than center does not work as it is overridden with a hardcoded TextAlignment.Center value.
See Openize.Slides.Slide.AddTextShapes:
textShape.Facade = _SlideFacade.AddTextShape(textShape.Text, textShape.FontSize, TextAlignment.Center, Utility.PixelsToEmu(textShape.X), Utility.PixelsToEmu(textShape.Y), Utility.PixelsToEmu(textShape.Width), Utility.PixelsToEmu(textShape.Height), textShape.FontFamily, textShape.TextColor, textShape.BackgroundColor);