string->llong doesn't like large numbers

Using Bigloo 4.1a

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Bigloo (4.1a)                                                            ,--^,
`a practical Scheme compiler'                                      _ ___/ /|/
Tue Feb 18 19:35:13 CET 2014                                   ,;'( )__, ) '
Inria -- Sophia Antipolis                                     ;;  //   L__.
email: [email protected]                              '   \    /  '
url: http://www-sop.inria.fr/indes/fp/Bigloo                       ^   ^
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1:=> (unsigned->string (string->llong "c1e093dd30490000" 16))
7fffffffffffffff
1:=> (unsigned->string (string->llong "41e093dd30490000" 16))
41e093dd30490000
1:=> (quit)

string->llong doesn't seem to like the top bit set.
Just the unsigned->string seems to work

1:=> (unsigned->string #lxc1e093dd30490000)
c1e093dd30490000
1:=>


Is this expected?

Thanks,
Todd D.