This is a follow-up of bug #132557 It appears that placeholder shapes with service names: - com.sun.star.presentation.TitleTextShape - com.sun.star.presentation.DateTimeShape - com.sun.star.presentation.FooterShape - com.sun.star.presentation.SlideNumberShape ... Are unable to have custom shapes in Impress. (i.e. can't be ellipse, triangle etc.). These presets get specified in OOXML with <a:prstGeom prst="ellipse"/> inside spPr (shape properties). If we opt in and import them as custom shapes, it is recognized by the document model as missing title/subtitle in a slide and some new placeholders appear on the slide. It is possible to disable these for footer placeholders, so in the implementation, we import footers as custom shapes only to slides. At the initial import correctly displaying the slide. But if the imported slideshow gets edited and a new slide with footers gets added, the footers in the new slides would become rectangles. (This is because we can't import footers into the master slides as custom shapes - doing so would mean that they would get inserted to each page without considering any placeholder context) A better fix would be implementing custom shape support for placeholder shapes. It would be a large feature work.
That requires a change to ODF. To be usable for title shape or outline shape, it needs the attribute 19.393 presentation:class and 19.411 presentation:placeholder. But that is currently only usable with <draw:frame> 10.4.2 and <draw:page-thumbnail> 10.3.14. However, the <draw:frame> element has a 10.4.3 <draw:text-box> child element. That can by itself have corner radius and it may contain any shape as child element. But such full support for shape child elements is currently only implemented in Writer. (bug 35033 and likely more). Having rounded corners would by nice. But does people really need to put a title or an outline into an arbitrary shape?