Adding values returned by GREATEST

Hello,

i have a question regarding the GREATEST function of mysql.

I would like to add the values returned by GREATEST function is mysql, so a
query is like below:

For example table t has 6 fields with values as follows: A = 1, B = 3, C=0,
D = 0, E = 1 and F = 0 and I run a query:

SELECT
GREATEST (A, B, C) AS G1,
GREATEST (D, E, F) AS G2,
(
GREATEST (A, B, C) + GREATEST(D, E, F)

) AS Total
FROM t

The result row I expect is: 3, 1, 4
But I get 3, 1, 6

However when I run the query like below I get correct results as total
being 4:

SELECT
(
GREATEST (1, 3, 0) + GREATEST(0,1,0)

) AS Total

So what I noticed is as I add result from GREATEST function, the result is
adding 1 for each GREATEST call I have in total. So, if I change my query
as below:

SELECT
GREATEST (A, B, C) AS G1,
GREATEST (D, E, F) AS G2,
(
GREATEST (A, B, C) + GREATEST(D, E, F) + GREATEST(D, E, F)

) AS Total
FROM t

The results will be 3, 1, 8

GREATEST (A, B, C) + GREATEST(D, E, F) + GREATEST(D, E, F) is calculated as

GREATEST (A, B, C)  = 3 + 1
GREATEST(D, E, F) = 1 +1
GREATEST(D, E, F) = 1 +1

So the total is 8.

I have tried online to search for this type of behaviour but no luck. Can
anyone please explain this.

Many Thanks,
SK