Note: probably earlier versions are also affected, I didn't check.

Max values for rowid_merge_buff_size are:

64-bit unix 9223372036854775807 (type BIGINT UNSIGNED)

32-bit unix 2147483647 (type INT UNSIGNED)

64-bit win  4294967295 (type INT UNSIGNED)

32-bit win  2147483647 (type INT UNSIGNED)

It's not dangerous or anything, just weird.
BIGINT UNSIGNED with the max value 9223372036854775807 is strange in itself, but not unique (at least there are also myisam_max_sort_file_size and aria_max_sort_file_size). However, it seems to be the only variable where 9223372036854775807 translates into 4294967295 on Windows. Just want to make sure it's intentional.