I probably just did something wrong myself, but posting in case someone else has had the same problem and there's somehow legitimate problem in wiki.
I tried making improvements to "Water Terrain" -page (using "Edit source" that I'm used to.) I had finished writing them and pressed "Preview." However, I quickly realized the preview was from the original version of the page, the one I saw before starting the edit. I frantically assume I must have done excess/wrong clicks and try to go back to page with my edits on it, but it no longer exist. Feel really defeated and don't have the energy to re-do the edit from scratch.