Hey Alex!
Well I just tried with Mac and Chrome. I think it's probably not related to the operating system. For me it works without the textbox disappearing. Oftentimes when the textbox disappears it means there was malformed markup in that textbox. Like a wrong " quotation mark somewhere, it's hard to say.
Can you replicate the problem and post the whole code that is in your textbox before it disappears?
I know for sure if you put a quotation mark into the code at the wrong place or when you write class="hey instead of class="hey" then that makes the content unreadable.
