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Mediawiki automatically adds a <p> at the first line break in a table cell.  The
following code produces the unintuitive result shown at the referenced URL.

{| style="border: 1px solid #aaa"
|-
| a
b<br>
c
d
|-
|}

Intuitively, "b" should be on the same line as "a", just like "d" is on the same
line as "c".  Instead, the <p> forces a blank line that doesn't correspond to a
blank line in the wiki markup.  The closing </p> forces a blank line after "d".

{| style="border: 1px solid #aaa"
|-
|
a
b<br>
c
d
|-
|}

If "a" is moved to the next line, it trades places with the first blank line,
leaving extra space at both ends of the cell.  In this situation, "b" is on the
same line as "a", as it should be. 

{| style="border: 1px solid #aaa"
|-
|
a
b<br>
c

d
|-
|}

Inserting a blank line produces the expected behavior that a blank line in the
markup corresponds to a blank line in the output.