Steps to reproduce: Edit https://hu.wikipedia.org/wiki/Szerkeszt%C5%91:Tgr/graph_teszt, change something in the static image (e.g. the text in .signals.init and save.
Expected result: you see the static image with the US map and the text
Actual result: the image replaced with the browser's "broken image" icon, but it appears correctly after a page reload
Some sort of race condition with the image rendering of the REST API, I presume.