The following code results in a "Implicit conversion changed sign of value" warning being emitted by the compiler:

int64 test = -9223372036854775808;

According to http://www.angelcode.com/angelscript/sdk/docs/manual/doc_datatypes_primitives.html, that's a legitimate value for an int64 and I see it print correctly using:

print(formatInt(test, ""));

This code does not result in the warning:

int64 test = -9223372036854775807;

UPDATE: Version 2.29.2 WIP - 2014/07/21, rev 1985, 32-bit linux.