Slight spanner problem

[Doug Asherman]

I'm not quite sure how to describe this: if it's not clear, please let 
me know.

I have a score that has a lot of words spanning bar lines; but the 
person I'm doing it for doesn't want any words outside the confines of 
the bars, so I've set up the Lyrics context like so:

\context {
  \LyricsContext \consists "Bar_engraver"
  \override BarLine #'transparent = ##t
}

and the elements are grouped like so:

<<
  Staff
  Lyrics
  Staff
  Lyrics
>>

No problems with the words; they're within the bar lines (even though 
the bar lines aren't visible). But if a line of music ends with a tie 
and the word it ends on has an extender spanner, then the extender juts 
out a bit beyond the (invisible) bar line.

Also, when I'm compiling the source, I get:
"programming error: round filled box vertical extent smaller than blot; 
decreasing blot"

The spanner problem is extremely slight; but I wondered if there was 
perhaps some other way to keep the words inside the bar lines.

Thanks,

Doug