Are identical strings ever not equal?

I'm sure this has been discussed but I can't find it and can't recall the answer

is it ever possible for two strings that are composed of the same characters to return false when comparing for equality?

A simple test
local s1:string = "string"
local s2:string = "string"
if(s1=s2)
print "true"
else
print "false"

shows that they are considered to be equal. I need to know though if any circumstances could make that return false.