It tried to upload a file when I have just clicked on "Import Data File *" test

Rep. steps
1. Login and navigate to Import Multi-value Custom Data page
You can easy move to mentioned page entering to this link
<site url>/civicrm/import/custom?reset=1
In my cases, I was able to reproduce the issue on the following server http://dmaster.demo.civicrm.org/civicrm/import/custom?reset=1
2. Just click on "Import Data File *" test and file uploading action will be immediately activated

Please note that the same behavior I noticed on below elements too
When you click on "Multi-value Custom Data *" test element the "Select" element will be activated, or clicking on "Import Field Separator *" test element the "Input" element will be activated