Did you ever experience this? Does it make sense to register this as a bug and how would I do this?
For one of my screens I have now this situation for the 2nd time: I insert a CupertinoButton with Text as a child, however, the text does not show up. In the 1st occurrence, 2 pixels of text appeared to be rendered (I saw 2 dots). I have also copied a CupertinoButton from another line and left it unchanged. No change, text does not appear. If I then only change the widget name from CupertinoButton to FlatButton (leaving everything else untouched), the text appears.
Since CupertinoButtons are typically working for me, I guess I would have to submit the whole project for a bug report, since isolating the issue does not to be appear like a straight forward job.