Yep, it's a known issue - don't rely on them.
Instead, split the string yourself (at each \n) and store the parts in a table which you'll iterate through and call drawString on each parts.

example :
local myTable = myString:split("\n")
    for i, str in ipairs(myTable ) do
        gc:drawString(str, 5, 5 + i * 10, "top")
    end