This is a stupid Gotcha, like most Gotchas it is just irritating and something that frankly could have designed better.
If you set the Text property of a DataGridViewButtonColumn it doesn’t show up in the designer. Further more it doesn’t show up at run time in an empty DataGridView either! So it is quite misleading, it makes you feel like you didn’t do something right.
Don’t worry, if you set the Text property then you indeed did set the correct place. The gotcha is, that the text won’t show unless you have rows in your DataGridView, whether you load them from a data source or you add a row manually.
No bug here, just a minor annoyance.