Problems with full screen mode and Safari

Hi, sometimes when sighted people are looking at something with me in Safari they want to make the window larger, they may call this maximising it which I take to be the same as putting it into full screen mode. So I put Safari into full screen mode and whenever I do this then switch away to another app and back again, Safari seems to lose the window which was open before I had switched away. So for example I may have two windows open in Safari, both of which may contain several tabs. If I am looking at window 1 in full screen mode then we've finished working, I switch away to another app; then when I switch back to Safari, it's showing window 2 and it seems like window 1 has disappeared entirely. Today a sighted person managed to get it back for me but couldn't explain how they did that, and I wasn't able to switch to window 1 either by the command apostrophe keystroke or with the window chooser. Has anyone else experienced this while using full screen mode in safari?