Rblx.lua Engine Vs Lua Stand-Alone Engine - Functions don't work the same way?

Today I finally downloaded the lua engine. ^-^ For the first code I tried, I used the code below:

function returnNumPlus1(num)
	return num + 1
end

print(returnNumPlus1(0))

print(returnNumPlus1(9000))

local func1 = returnNumPlus1
print(func1(11))

I tested both codes; the Rblx.lua engine fired, while the stand-alone lua engine returned an error. The error is as follows:

stdin:1: attempt to call global 'func1' (a nil value)
stack traceback
		stdin:1: in main chunk
		[C]: ?

Why is it that Roblox's worked, while the lua stand-alone engine errored? I can't see why one works while the other doesn't? Why is that?

Thanks for reading. ;)