Losing table vertical alignment when converting ditamap to book

FrameMaker Version: 12.0.4.445 (latest, part of TCS5)

1. I have a structured project, where several XML files have been arranged into a ditamap.
2. For one of the XML files, I have a table, where I need to set Cell Vertical Alignment of the cells to MIDDLE.
3. So using Paragraph Designer> Table Cell, I change the entries from Top to Middle (The defaults were Top).
4. With the ditamap pane selected, I then go File menu >> Save Ditamap As
5. I save the ditamap as "Book 12.0 with fm components (*.book)" file type.
6. In the resulting book, the XML files are now .FM files.

However, at this point, when I open the .FM file that has the table, the cell styles have reverted to TOP.

I've searched high-and-low for a similar issue. This is looking like a bug to me, but can someone confirm?

Thanks