Finance BR GetDataCell returns value, but report loses formatting on that column.

I have a column in my cube view with cell values retrieved using a custom (GetDataCell(BR#[...])) call. The value is returned just fine, but the cells in that column are losing formatting that should come from the row format.

If I use an XFBR dashboard data string function to return the GetDataCell call as text, it also works and the formatting is retained.

If anybody has a suggestion as to why using the Finance rule to return a single value is replacing the formatting, that would be appreciated as that is my preferred approach.

Thanks!