The form in import.vm says
When the administration application is absent, the action is "admin" so when you try to import you are sent to the bad action.
It displays the message:
Importing xwiki-application-administration-1.2.xar: Error while preparing importing
- 0 Document(s) installed
- 0 Document(s) skipped
- 0 Document(s) with error
As if the import failed when it fact it was not even started.
The form needs to call the import action