This shows up with linux 2.4.18, cmucl 18e and up to date anoncvs slime; the problem is that every time you send a buffer larger than 4092 bytes, read-sequence will only get the first 4092. I've attached a fix that works for me, but might not be the best solution in the case of an actual network connection. The change basically adds read-sequence-fully, and modifies read-next-form to use it.