Pushup Element: CSS selector works with IDs but not with class names

[porg]

Reproduction

• Create a page with these block setup
  • Columns block
    • Left column
      • A few paragraph blocks. In total longer than the Image height in the right column.
    • Right column:
      • Sticky block (wrapping the Gutenslider block)
        • Image block wrapped within Sticky block
• Headings block
  • Acts as the pushup block
  • Has ID #media-text-block (via Advanced > HTML Anchor) and class .wp-block-heading in the HTML output
• Other blocks follow

Observation (possibly bug)

• Sticky block → Pushup element
  • ✅ Setting a CSS ID #media-text-block works
  • ❌ Setting a CSS class .wp-block-heading fails to select the pushup element
    • This puzzles me a bit, because the hint text of "Pushup element" says e.g. '#footer', '.widget-bottom', etc. which gave me the impression that both IDs and classnames are allowed to select the pushup element.

Screen Recording

WordPress.Sticky.Block.Pushup.Element.can.be.selected.with.ID.but.not.with.CSS.class.mp4

[porg]

Bump.