weird line in histogram

Dear All,

I try to plot a histogram, which succeeds nicely, but I also get a
strange line in the same plot. Does anybody know why this is the case,
and what to do about it? Here is the code:

    n, bins, patches = hist(res,bins = 10, cumulative=True, normed=False)
    l = plot(bins)

res is a simple list. The line through the plot runs from min(res) to
max(res), as it seems.

Thanks in advance.