If the block-formatted content begins with a list (or any other wikimarkup that is dependent upon a specific markup character being at the beginning of a line) then due to a bug in MediaWiki, a <nowiki /> must exist before the list (or whatever) starts. Compare:

  code result
FAIL
 {{Block bug documentation|1=
 *Firstly, ...
 *Secondly, ...
 *Thirdly, ...
 }}
This output only works when this doc snippet is transcluded.
Works as intended
 {{Block bug documentation|1=<nowiki />
 *Firstly, ...
 *Secondly, ...
 *Thirdly, ...
 }}
This output only works when this doc snippet is transcluded.

To embed a table in block markup like this, the block template's content parameter must be named or numbered and include the self-closing noinclude – as in |1=<nowiki /> – then every | character in the table markup must be escaped with {{!}}. An alternative is to use explicit HTML <table>, <tr>, <th>, and <td> markup.