>>Will _memberdata be an 'innocent' property as long as I don't use it?
>
>It'll as long as it not exceed 255 characters.

Well, I've done some research on this one and I must conclude that it's a very important one. It became clear to me that it is also used for the Favorites tab of the Properties Window.

The first time there is no _memberdata property. RightClick on a property or method in the Properties Window, choose 'Add to Favorites Tab'. Now the _memberdata property will be created. Each next time something is added to the Favorites Tab _memberdata will be extended. It will exceed 255 characters very soon. And from that moment on the form will no longer open in vfp7.

This is crucial for me and kind of forces me to make the jump to vfp9 and not jump back anymore. Perhaps this isn't a problem for prg-based stuff (like libraries), but, as you said, it is a problem with forms and classes. Unless, of course, the Favorites Tab is not used. But that requires constant awareness of the problem.

I wish it had not been like this. Esp. some classes are shared by several applications. Some of them are ready for further development in vfp9. Others will, for the time being, be further developed in vfp7. Now I'm forced to fork classes. Pity.

Update: All is not lost when the form doesn't want to open anymore in vfp7. Simply open it in vfp9, empty the _memberdata property and quit. Now you can open it again successfully with vfp7.

Update2: Some additional research here surprised me. It appears that I have asked the same question back in 2004. I have completely forgotten that. To my defense I can say that I had bigger worries then vfp-conversion at that time. See Does vfp9 change frx, vcx, scx, etc.? Thread #910378