Fractional share purchases

[Ben]

Hi there,

I've subscribed to a dividend re-investment programme, which
results in the purchase of fractions of shares. I thought I
could account for this by going into the commodity editor
and setting the value of "fraction traded" to "1/1000".

However, GnuCash rounds up the amount of my fractional
shares 
to 2 (should really have been 1.729) and changes the price
accordingly. 
Now my shareholding is overstated by 0.271 shares; not
exactly 
significant in the great scheme of things, but I'd still
like to 
get this right.

Are there any other settings to be made for this to work?

Ben