I built the mausoleum, then clicked "Back", because I didn't want to Ascend yet. Then I clicked the mausoleum again. The result: it's now in an infinite loop of popping up the "Wonder complete" screen.
Reloading the page, or exporting-and-importing the save game, don't fix this.
Save game, currently caught in infinite loop: https://www.dropbox.com/s/9felkomp3ceonik/legacySave.txt?dl=0
Instructions: load save game. "Mausoleum" window will pop up. Click "Back" or the "X". "Mausoleum" window will pop up again.
(I'm using Firefox 52.0.1 on Mac OS X 10.12.3, in case that turns out to be relevant. I haven't tested in other browsers.)