Expression Bug?!

[js2002]

I put this into a hand report:

char_length(cash_hand_summary.str_aggressors_p) >= 3 AND cash_hand_player_statistics.position BETWEEN substring(cash_hand_summary.str_aggressors_p from 2 for 1)::int and substring(cash_hand_summary.str_aggressors_p from 3 for 1)::int

And put

cash_hand_player_statistics.position = 8
substring(cash_hand_summary.str_aggressors_p from 2 for 1)::int = 0
substring(cash_hand_summary.str_aggressors_p from 3 for 1)::int = 8

So I see Player/Hero in BB Position and the 2bettor in BU Position. Thats correct so far.
Now the problem:

cash_hand_player_statistics.position BETWEEN substring(cash_hand_summary.str_aggressors_p from 2 for 1)::int and substring(cash_hand_summary.str_aggressors_p from 3 for 1)::int
in real number:
8 BETWEEN (0 and 8) = true

is that correct?
I think only 1-7 are between? Thats the SQL definition!
(I googled some text sql between examples, there 0 is in the range but never 8.)

bug or not?
define between and not between please.