Text Function - insert() behavior

I have encountered a weird behavior related to insert() function. My use case is I am trying to insert 3 new values at the top of the list. 

E.g. Initial list is {"W","X","Y","Z"} and I try the insert command like insert({"W","X","Y","Z"},{"A","B","C"},{1,2,3})

But this command doesn't yield the expected result and yields output as {"A", "W", "B", "X", "C", "Y", "Z"}

Again I tried like this : insert({"W","X","Y","Z"},{"A","B","C"},{1,1,1}) and output is as expected : {"A", "B", "C", "W", "X", "Y", "Z"}

Can someone help me understand why {1,1,1} worked but {1,2,3} didn't?

Thanks in advance!