Compiling the following code seems to cause a failed assertion:

void test(uint8 x) { print("test 8: " + x); }
void test(uint16 x) { print("test 16: " + x); }
void test(uint32 x) { print("test 32: " + x); }
void test(uint64 x) { print("test 64: " + x); }

void Main()
{
	test(uint8(0xFF));
	test(uint16(0xFFFF));
	test(uint32(0xFFFFFFFF));
	test(uint64(0xFFFFFFFFFFFFFFFF));
}

Ignoring the failed assertions, we do seem to get the expected result:

[   ScriptRuntime] [23:23:44]  test 8: 255
[   ScriptRuntime] [23:23:44]  test 16: 65535
[   ScriptRuntime] [23:23:44]  test 32: 4294967295
[   ScriptRuntime] [23:23:44]  test 64: 18446744073709551615