Why does this cause a stack overflow? [LUA]

function printtable (t)
    for i,v in pairs (t) do
        strbuf = ""
        for iter=1, tabs, 1 do
            strbuf = strbuf .. '\t'
        end
        print(strbuf, v)
        if type(v) == "table" then
            tabs = tabs + 1
            printtable(v)
        end
        tabs = tabs - 1
    end
end

tabs=0
printtable(_G)

It shouldn't recurse that much.

Further fucking source of confusion: Why isn't lua global.lua | head -n 1000 | uniq -d detecting these obvious duplicates? init.lua seems to be the source of the circular definition, btw.

./?.lua;/usr/local/share/luajit-2.0.0/?.lua;/usr/local/share/lua/5.1/?.lua;/usr/local/share/lua/5.1/?/init.lua
table: 0x40635b30
table: 0x40636728
function: builtin#33
function: builtin#36
function: builtin#30
function: builtin#34
function: builtin#31
function: builtin#32
table: 0x4063a568
function: builtin#153
function: builtin#154
function: builtin#152
function: builtin#156
function: builtin#158
function: builtin#159
function: builtin#157
function: builtin#160
function: builtin#162
function: builtin#161
function: builtin#155
table: 0x4063aaa0
function: builtin#163
table: 0x40638a28
function: builtin#39
function: builtin#45
inf
function: builtin#41
function: builtin#64
function: builtin#44
function: builtin#49
function: builtin#63
function: builtin#59
3.1415926535898
function: builtin#62
function: builtin#57
function: builtin#60
function: builtin#38
function: builtin#40
function: builtin#55
function: builtin#48
function: builtin#59
function: builtin#47
function: builtin#58
function: builtin#37
function: builtin#61
function: builtin#43
function: builtin#52
function: builtin#54
function: builtin#51
function: builtin#42
function: builtin#53
function: builtin#50
function: builtin#46
function: builtin#56
table: 0x40636ac0
table: 0x40636f88
function: 0x4063ab48
./?.lua;/usr/local/share/luajit-2.0.0/?.lua;/usr/local/share/lua/5.1/?.lua;/usr/local/share/lua/5.1/?/init.lua
table: 0x40635b30
table: 0x40636728
function: builtin#33
function: builtin#36
function: builtin#30
function: builtin#34
function: builtin#31
function: builtin#32
table: 0x4063a568
function: builtin#153
function: builtin#154
function: builtin#152
function: builtin#156
function: builtin#158
function: builtin#159
function: builtin#157
function: builtin#160
function: builtin#162
function: builtin#161
function: builtin#155
table: 0x4063aaa0
function: builtin#163
table: 0x40638a28
function: builtin#39
function: builtin#45
inf
function: builtin#41
function: builtin#64
function: builtin#44
function: builtin#49
function: builtin#63
function: builtin#59
3.1415926535898
function: builtin#62
function: builtin#57
function: builtin#60
function: builtin#38
function: builtin#40
function: builtin#55
function: builtin#48
function: builtin#59
function: builtin#47
function: builtin#58
function: builtin#37
function: builtin#61
function: builtin#43
function: builtin#52
function: builtin#54
function: builtin#51
function: builtin#42
function: builtin#53
function: builtin#50
function: builtin#46
function: builtin#56
table: 0x40636ac0
table: 0x40636f88
function: 0x4063ab48
./?.lua;/usr/local/share/luajit-2.0.0/?.lua;/usr/local/share/lua/5.1/?.lua;/usr/local/share/lua/5.1/?/init.lua
...etc