File format import compatibility: when migrating a GTG 0.6 file ("0.5" format) to 0.7, tags hierarchy is not preserved (no nested children / parents tags)

[nekohayo]

Testing the latest git master version through ./launch.sh -s a_copy_of_my_gtg0.6_dataset, GTG tries to convert the gtg_data.xml file that starts like this:

<?xml version='1.0' encoding='UTF-8'?>
<gtgData appVersion="0.5" xmlVersion="2">
  <taglist>
    [various other tags]
    <tag id="f351b578-eddf-4291-8d39-090c03129194" name="travel" icon="🗺️" nonactionable="False"/>
    <tag id="9704db6e-6e52-45c5-bc64-cb38e3091458" name="waitingfor" icon="⏱️"/>
    <tag id="9946977a-653c-47dc-bdb2-865eebde5a88" name="conferences" parent="travel"/>
    <tag id="cc1423e2-15f0-4e3a-bd9f-688057333b11" name="guadec" nonactionable="False" parent="conferences"/>
    [various other tags]

…into this:

<?xml version='1.0' encoding='UTF-8'?>
<gtgData appVersion="0.7-dev-b8581b12" xmlVersion="2">
  <taglist>
    [various other tags]
    <tag id="f351b578-eddf-4291-8d39-090c03129194" name="travel" icon="🗺️" nonactionable="False"/>
    <tag id="9704db6e-6e52-45c5-bc64-cb38e3091458" name="waitingfor" icon="⏱️" nonactionable="False"/>
    <tag id="9946977a-653c-47dc-bdb2-865eebde5a88" name="conferences" nonactionable="False"/>
    <tag id="cc1423e2-15f0-4e3a-bd9f-688057333b11" name="guadec" nonactionable="False"/>
    [various other tags]

As you can see, it completely throws away the parent="some_other_tag" hierarchy data in the conversion (as a result, all tags are shown flat on the same level in the sidebar), even though the app itself is capable of setting tags' hierarchy in the sidebar (and remembering them on the next startup), so this seems to be just a file format migration issue?