DrawLine-log-vs-linear-scale-WL7-vs-WL6

Hello, I notice some problems plotting a line with log Scale depending the number you put in the box.
For example you can check:

Ticker: A (Agilent Tech). Yahoo data, all data, monthly.
int a = 143;
int b = 195;
DrawLine( a, bars.Low[a], b, bars.Low[b], Color.Black,1, LineStyles.Solid,"Price", true,true);

Log Scale
Spacing: 9 (line near march 2009)
Spacing: 8 ( line far march 2009)
Spacing: 7 (line disappears!!)
this does not happen with linear scale WL7 (OK)
this does not happen with Log scale W6(OK)
this does not happen with linear scale W6(OK)




and it's more strange with a code I made to calculate some trend lines
the same line: LOG scale spacing 6 and spacing 5 ( although I guess the problem is the same)