This happened to me, as well, initially. Its frustrating. And yes, it will delete everything if it happens.
So much done with Drupal (as I assume this forum is, as well) seems to be too complex for its own good.
They keep adding things to fix other things, then if there is an issue with that, they add more, to fix the thing that fixes the other thing. Maybe a module to fix some of that, and then another model to adjust the items in the previous module, and possibly another module to fix some of the things in the module that fixes some of the things in the previous module which fixes some things in the additions, that fixes some other things from the additions before to fix something else. Too many things go off on separate tangents.
They built a monster.
They should strip it down and simplify things at a core level. When you make things too complex, there is no way to keep up with the problems that will come up, it just gets more and more complex. Microsoft did similar, where if you try to report a Windows error message to them, they will basically tell you "Uh, well we don't know wtf that means".
When something that is supposed to be an intuitive UI/GUI for web design basically tells people they have to hack code at the server level to do something as simple as a color adjustment, clearly that defeats the whole point.
In reply to this forum, just keep changing the subject and some text, and use Save (which should be "Post" but I digress), and not Preview. Preview/Save never seems to work.