Weird results from SUMIF

I don't see anything in the formula that explains the incorrect result. You have not shared all of the data, so we cannot independently verify. My guess is that something about the summing condition (what is in A:A and A1) is causing those two copies of the function to sum all 6 of those values. I observe that 10.54+12.81-2-2-5-5=9.35. Something about your condition is not distinguishing between the two sums, but is combining those 2 sums together.

Many thanks! I feel embarrassed not to have realised that the two sets of figures together totalled 9.356 - but that, as you suggest, makes the answer clear. Column A is formatted as text; and, as a total amateur, since we're told (in the 'Format cells' window) that 'Text format cells are treated as text even when a number is in the cell' , I assumed that if A1 held '1.1' and A27 (as it happens) held '1.10', they would be distinguished as different text strings , but obviously that doesn't happen, and they've been treated as numbers , and therefore identical.
Anyway, it's something I can easily correct, and many thanks again for so promptly sorting me out! SOLVED.