An unfortunate discovery

[Adrian Custer <acuster gmail com>]

Hey all,

I just stumbled on something (ie Adrian messed up) that surprises me a
little. In a cell I had the formula:
        =F71:J71+M71
which evaluated to:
        =J71+M71
rather than the calculation I was hoping for:
        =sum(F71:J71)+M71
with unfortunate consequences. 

However, I am quite surprised that the first of these is legal.
Actually, playing around a little now, I am even more surprised. If the
calculation is done in F79, one gets a different answer (=F71+M71) than
if the calculation is done in J79 (=J71+M71).

Is this a well known behaviour of spreadsheets which I am only now
discovering? In this case, does this have a name?

cheers,
--adrian