Suppose you have the following doxygen code:

/** \page my_page_2 Another page

<table>
<tr><th>Byte no</th><th>Bit</th><th>Function</th></tr>
<tr><td>0</td><td>0x01</td><td>Energy</td></tr>
<tr><td>0</td><td>0x02</td><td>Volume</td></tr>
<tr><td>0</td><td>0x04</td><td>Temperature T1</td></tr>
<tr><td>0</td><td>0x08</td><td>Temperature T2</td></tr>
\if ADVANCED_METER
<tr><td>0</td><td>0x10</td><td>Phase</td></tr>
\else
<tr><td>0</td><td>0x10</td><td>Reserved</td></tr>
\endif
<tr><td>0</td><td>0x20</td><td>Flow</td></tr>
</table>

 */

In the HTML output, the \if-line causes </p><p class="endtd"></p> to be inserted into the last preceding <td> adding an empty line to the cell.
In the tex output an empty line is added to all cells on the last row.

The same effect occurs at the \endif.

Bug 576701 discusses <p> in table cells, but seems to be a different behaviour since it talks about enclosing all table data in paragraphs, not adding an empty paragraph in some cells.