Consider the following transcript.

        Objective Caml version 3.10.0

# string_of_bool true == string_of_bool true;;
- : bool = true
# String.fill (string_of_bool true) 0 4 '@';;
- : unit = ()
# string_of_bool true;;
- : string = "@@@@"

Perhaps this has been discussed before, but I found this to be disturbing.
It seems easy enough to fix this problem, so that, for example, print_string
(string_of_bool true) always does the same thing.
The "correct" strategy seems to be used for string_of_float infinity:

# string_of_float infinity;;
- : string = "inf"
# string_of_float infinity == string_of_float infinity;;
- : bool = false

Nathan Mishra-Linger