It was the result of a discussion in the Lazarus forum (https://forum.lazarus.freepascal.org/index.php/topic,54987.msg408763.html) that there exist malformed dbf files which are read correctly by LibreOffice Base or third-party dbf viewers, but result in incorrect float values when read by the TDbf fork of FPC. The sourceforge version is affected in the same way.
For a fix, please see my patch in the Lazarus/FPC bug tracker: https://bugs.freepascal.org/view.php?id=39009