I have my UI language set to English. Today I merged several items which had English labels into items which did not have English labels. I noticed at least 4 times that, after the merge, the page title (the one just above the table with the labels/descriptions/aliases) still showed "No label defined" instead of the English label. Refreshing the page didn't help, only purging the page fixed it.
I'm not sure if it happens every single time, but I was also able to reproduce it on test.wikidata.org on my first try at https://test.wikidata.org/wiki/Q2426

