Hello.
This happened today. In English Wikipedia, when "Wikitext syntax highlighting" is enabled, the "Replace all" button in the "Search and replace" dialog box (part of the default Wikitext editor) does not work. Fortunately, tapping the "Replace" button multiple times still does the trick.
As a precaution, I reset all my settings to default before testing this. (Mind you, resetting the settings is a major difficulty, seeing as I have to go back and set them to what they were, especially since I do it often. I wonder if there is a way to save and restore them.)