RecordSource - bang.boom.gone

In Visual FoxPro every object belongs to a particular data session. Under normal circumstances this is the data session in which the object is created. The exception are objects that have an intrinsic data session, namely Form, FormSet, Toolbar, and Session. Instantiating these objects may create a new data session in which these objects are then built.
The grid is unfortunately slightly more pro-active. Whenever the record source cursor disappears even for the fraction of a nanosecond, the grid responds immediately. Closing a cursor is an obvious way to hide a cursor. Creating a new cursor in the same work area isn't as obvious, but still understandable. In both cases the grid responds by removing all columns and the RecordSource. On the visual front the grid turns into a white rectangle with a thin black border.

Changing the data session isn't all that obvious. Nonetheless, moving the form - and along the grid - into a different data session constitutes a change in visibility of the cursor. Consequently, the grid updates itself and blanks out the RecordSources property and all ControlSources.

Contrary to closing the cursor in the current data session the column objects remain, only the binding information is gone. As a result the grid looks much like before. Except that there's no record shown. The only visible clue is that the deleted mark column on the left side of the grid is black for all records instead of cleared as it was before.

If this happens to you in a grid where you don't always expect data to be shown this can be a bug that is hard to discover and hard to nail down. On a screen shot of your application, watch out for the deleted mark column.