minimum-length property has no effect on last bar of system

[address@hidden]

Spanners' minimum-length property does not work on the last bar of a system.

\version "2.17.10"

tslong = {
 \once \override TextSpanner.springs-and-rods = #ly:spanner::set-spacing-rods
 \once \override TextSpanner.minimum-length = #30
}

{
 \override TextSpanner.to-barline = ##t
 \repeat unfold 4 a1
 \tslong
 a1\startTextSpan
 \tslong
 a1
 \stopTextSpan \startTextSpan \break
 a1 \stopTextSpan
}