As reported on Commons: https://commons.wikimedia.org/wiki/Commons:Village_pump#Special:Upload_prepending...
Every upload with the classic upload-form got prepending the first headline {{int:filedesc}} twice (s. cleanup bot https://commons.wikimedia.org/wiki/Special:Contributions/OgreBot_2 , seems since 2018-02-07T20:37:02)
@TheDJ mentioned https://gerrit.wikimedia.org/r/#/c/398845/ as the reason.
Seems conrete: https://gerrit.wikimedia.org/r/#/c/398845/7/includes/specials/SpecialUpload.php