Editing forum opens an opacity 0.01% pop up (sometimes, mobile Android 5)

You can write but you don't see what are you changing or how to save it. Accordingly when you try to go back to the forum or somewhere else, there as a pop up warning you that you are going to lose your changes which is confusing for the final user (as (s)he doesn't know an editing popup was opened because (s)he couldn't see it)