If I hadn't seen this behavior, I would never have believed it!
Open the attached xlsx file then insert a blank row before row 5.
After the insert, your spreadsheet will look like this:
A B C
1 1 3 =a:a*b:b
2 1 3 =a:a*b:b
3 1 3 =a:a*b:b
4 1 3 =a:a*b:b
5 <notice, this row is completely empty, and there is no formula in cell C5.
6 1 3 =a:a*b:b
now, type "2" in cell A5 and "4" in cell B5.
excel MAGICALLY inserts the formula =a:a*b:b in cell C5.
To me this is an interesting discovery, but I cannot seem to control it.
For instance, If I manually type those values and formulas into a new spreadsheet, the behavior does not repeat.
But, if I copy the cells to the new sheet, the behavior does repeat. Clearing formats and conditional formats, does not change behavior.
Does anybody have any idea what is going on?
p.s. If I could control this feature, I think I would use it a lot. When I insert blank rows in the middle of spreadsheets, I often what the preceding row's formulas to be copied down.