TYPO3 Core

The above modification was removing to many linebreaks. The problem occurs only when the content element ends with one of the specified tags. The correction is then to add after:
$aC = count($blockSplit);
the following lines:
while($aC && !strcmp(trim($blockSplit[$aC-1]),'')) {
unset($blockSplit[$aC-1]);
$aC = count($blockSplit);
}
Perhaps removing just the last entry would be enough. In any case, the empty ending $blockSplit entry prevents the correct recognition of the tag as the last item of the content element.

Resolved in TYPO3 4.0