LibreCalc: Missing entry fields in dialog

Some of the user dialogs within LibreCalc (version 6.4.7.2, on Kubuntu 20.04) do not show entry fields. In particular, all dialogs for Conditional Formatting are affected.

See the attachment as an example for a bad dialog: There should be an entry field for the formula, but it is completely absent. That this is a bug has been confirmed at the LibreOffice forum:
https://ask.libreoffice.org/t/librecalc-conditional-formatting-for-separate-ranges/67552

Alas, I don't have a screenshot showing the correct dialog.

(I hope the package is right, but the search broke with an error message.)

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Description: Ubuntu 20.04.3 LTS
Release: 20.04

libreoffice-calc:
  Installed: 1:6.4.7-0ubuntu0.20.04.1
  Candidate: 1:6.4.7-0ubuntu0.20.04.1
  Version table:
 *** 1:6.4.7-0ubuntu0.20.04.1 500
        500 http://de.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:6.4.2-0ubuntu3 500
        500 http://de.archive.ubuntu.com/ubuntu focal/main amd64 Packages