It happens when converting from srt to sub and vice versa.
Code:
<i>first italic line</i>
<i>second italic line</i>
is correctly converted to:
Code:
{y:i}first italic line|{y:i}second italic line
But:
Code:
<i>two lines spanned
in single italic tag</i>
results in
Code:
"two lines spanned|in single italic tag"
which is incorrect - the italic tags are lost and replaced by quotes. The same happens if the <i> tag is not closed at the end of line (as produced by Subtitle Workshop).
Similar problem occurs when doing a sub -> srt conversion. The {Y:i} tag (capital Y) is taken only for the first line.
I think some parse-time convertor which replicates spanning and unclosed tags for each following line would be the best solution...