figured bass extender line problem

[Seng Liang]

Hi, I am using Lilypond version 2.7.12 for Windows 98 and I have some 
problems/bugs with extender lines in figured basses. Here is the file:

\version "2.7.12"


\relative {
<< 
\context Voice { \clef bass 
c,8 c c c d d e e f4 
} \context FiguredBass \figuremode {  \set useBassFigureExtenders = ##t 
<6 4>2 <6 5> <5 3>4 } >> }

Here, my intention is to put the figured bass <6 4> on the 1st beat, with the 
extender lines going until the end of the 2nd beat. Then <6 5> with the 
extender lines going to the end of the 4th beat. 3 problems came up:

1. Why is the extender line from "6" at the 1st beat continue until the 3rd 
beat and erasing the second "6"? How can I break the extender line on the 3rd 
beat, insert te "6" and continue the extender line until the end of the 4th 
beat? 
2. How do I make two extender lines that are vertically stacked coming 
extending from <6 4>?
3. In this version, the first number notated is at the top, ie. <6 4> means "6" 
is on top of "4". Why then is the order of <5 3> in the pdf file reversed? 
Thanks.
Yours sincerely,
Seng Liang.