On second look, it appears that you are mis-interpreting the output of DBCC PAGE.

As an optimization, when SQL Server changes the type of a column, it often just adds a new column and marks the old column as not used.

This is one of the reasons I try to avoid modifying table schemas.

If you are looking at page output in detail, you might be looking at the no-longer-referenced data, rather than the new column.

If you care to publish a reproduction script here (the connect item has limited visibility outside Microsoft and you) I would be happy to analyze it for you.

Paul