I've not seen this in practice.

You need some numeric accident involving a higher power operator like exponentiation.

In TXR Lisp I made exponentiation n-ary: you can do (expt x y z ...).

The associativity is right to left: it means

         ...
       z
     y
   x

rather than the less useful cumulative exponentiation of the same base:

  yz...
 x 

which can easily be obtained as (expt x (* y z ..)).

So, anyway, if you apply expt to small list of small operands, you can cons up a big number in rather a hurry.

If it is important to prevent a problem like this, a limit can be imposed on bignums (say, large enough for common cryptography to still work).