r.line stops partway through

[Simon Cox]

(Sorry folks - something about my drag and drop is
stuffing up the mailer it seems)

Who has used r.line to do raster -> vector conversion?
I am trying to use it on a scanned contour separation.
I am finding that it is working fine, but seems to stop
part way down my data - ie I get ok results down to a
certain row, and then nothing lower.  During running I get
a load of lines saying things like ...