AH Formatter / XSL Formatter
Q&A

Your FO is as follows:

<fo:list-item>
  <fo:list-item-label ...>
    <fo:block><fo:inline baseline-shift="super">Label</fo:inline>:</fo:block>
  </fo:list-item-label>
  <fo:list-item-body ...><fo:block>Body</fo:block></fo:list-item-body>
</fo:list-item>

XSL Formatter works correctly.

In the W3C Recommendation for XSL-FO, the initial value of relative-align is before. Therefore, list-item-label and list-item-body are aligned at each before-edge position. The line-area including baseline-shift="super" is higher. The baseline position of line-area has fallen.

If relative-align="baseline" is specified for fo:list-item, the baseline position of list-item-label and list-item-body is the horizontal.