2.5.18 bar line thickness error(?)

[Stan Sanderson]

Mac OS X, 10.3.8, Lilypond v. 2.5.18 through Fink

I have been coding a number of Bach chorals as brass quartet pieces. I 
am using a staff group arrangement. With version 2.5.18, the bar lines 
between staves is slightly thicker than the bar line within the stave. 
The difference is especially evident at the ends of the systems. A 
final bar line, \bar "|." has a wavy appearance.

This was (and is) not the case with v. 2.5.17, to which version I have 
reverted. Is this a bug or a feature?

Stan