PageMediaDimensions triggers a warning "unexpected PageMedia case in LoadDataFile()"

In Debian, since the upgrade to 3.1.1-1, when I run a command like

pdftk input.pdf update_info_utf8 info output output.pdf

where the info file contains

PageMediaBegin
PageMediaNumber: 1
PageMediaRotation: 0
PageMediaRect: 0 0 595.28 841.89
PageMediaDimensions: 595.28 841.89

I get the following warning:

pdftk Warning: unexpected PageMedia case in LoadDataFile(); continuing

This is PageMediaDimensions that triggers the warning. Note that it is present in the data generated by

pdftk input.pdf dump_data_utf8

It seems that

        if (buff.startsWith(PdfPageMedia.BEGIN_MARK)
            || pagemedia.loadNumber(buff)
            || pagemedia.loadRotation(buff)
            || pagemedia.loadRect(buff)
            || pagemedia.loadCrop(buff)) {
          // success
        } else { // warning
          System.err.println(
              "pdftk Warning: unexpected PageMedia case in LoadDataFile(); continuing");
        }

in LoadDataFile() from data_import.java doesn't match

  static final String PREFIX = "PageMedia";
  static final String BEGIN_MARK = "PageMediaBegin";
  static final String NUMBER_LABEL = "PageMediaNumber:";
  static final String ROTATION_LABEL = "PageMediaRotation:";
  static final String RECT_LABEL = "PageMediaRect:";
  static final String DIMENSIONS_LABEL = "PageMediaDimensions:";
  static final String CROP_LABEL = "PageMediaCropRect:";

from PdfPageMedia.java.