Cell Ref. in Formula changes automatically

[Guest]

My formulas are changing automatically and I can't figure out how to turn off
the feature. Example;

Columns C thru K contain numeric values. Column M contains a the formula
SUM(Cx:Ex) where x is the row #. As I'm keying data in cells C5, D5 & E5
everything is fine. When I key a number into F5 however the formula
automatically changes to include column F (i.e. SUM(C5:F5)). Excel makes the
assumption that just because there's a number in F5 that it should be
included in the formula. I've gone into Tools>Options>Error Checking and
played with the settings even so far as disabling 'background error
checking'. Now Excel changes my formula, it just doesn't call my attention
to it with a colored triangle in the upper left of the cell.

I know I'm missing something, any idea what?

 

[Guest]

Tools/Options/Edit/ turn off extend list formats and formulas.