Steps to reproduce:
On a slow connection, type "Katze" in the upper right search bar of the German Wikipedia and select the "enthält ..." option at the bottom of the autocomplete drop-down.
I see the results, with a white placeholder where the Advanced Search will appear. When the Advanced Search has finished loading, the white placeholder is replaced with the Advanced Search.
The search results are displayed directly below the default plain search field. When the Advanced Search has finished loading, the search results are pushed down and I lose my context or misclick.
If we'd go with Moriel's solution, it would have been estimated as 13+.