Go to any Maniphest task, Edit Related Objects -> Merge Duplicates In and try to select any task.
The window is simply closed without performing a desired action.
From quick bisecting it appears this issue was introduced by dcf3ca8e045.
In case it’s browser-related, i was testing this with current version of Chrome.
phabricator: 5d8ee504d645ba1a6d69c23b9cbad557e14b03ad (Wed, Jun 19)
arcanist: 7329bc7c32b995a7dce0319723857cbdf4f95a91 (Thu, May 23)
phutil: ada64585035e8fbdf5d0dd6abfb6c13e6b160b7d (Mon, Jun 17)