I am not sure how to turn off the help from Excel, but your problem regarding automatic selection of a range of cells reminded me what might be at play. However this is based on Excel 2003, so may not be applicable in your case.

When you are starting a formula but especially when you use the SUM function (via the toolbar icon), Excel seems to select a range of cells in a column that are "contiguous". If, for example, in a column you have a range a1 to a5 [A1:A5] and another range from a7 to a10 [A7:A10], and you are inputting a formula or SUM at A11, then Excel hi-lights the range [A7-A10] instead of [A1:A10] as the range [A7-A10] is the first contiguous range next to A11 where the formula is being started.

However, if you input <space> in cell A6, so it looks empty at a first glance (because <space> is not an obvious, visible character), and perform the same test, you will see that the range [A1:A10] are hilighted, since the rane [A1:A10] is a contiguous range!

I suspect that in your case the cell M10 has some value (even if it is a space character or something similar and left over from some other operation). Thus, first check if that assumpation is correct, i.e. if cell M10 contains anything, and perhaps try a Delete and/or Clean Contents operation on M10, then try out writing your formula and see if M10 is automatically selected.

I suspect that the issue you have is related to Formula Autocomplete function. When formula Autocomplete is enabled, as soon as you input "=" and type a letter a list of functions are displayed in a drop-down list for you to quickly select a function. However, in your case, you type "=" and then with the mouse you click on a cell, and since you have not continued your input into the cell with a character where Excel can help you out with formula autocomplete by displaying functions in a drop-down list (starting with the character you have input), but instead, you have selected a cell with your mouse, then Excel is probably trying to perform the formula autocomplete ability by hi-lighting a range selection... Perhaps you can Disable formula autocomplete.

You might want to test the above possibility by going to the Menu system, and then Options, choose 'Formulas', and selecting 'Working with formulas' group, and looking at the choices there and reconfiguring them!

In the meantime, if I find something specific regarding Excel's (idiotic) "helpful" hand :-) I'll post it here.

**Edited by daremo, 28 February 2012 - 09:19 AM.**