Yes, it's the SMCorders table.
I have run umpteen tests on this - including many live purchases - and I simply can't replicate it, yet it's happening on a daily basis for a lot of other people, but not for all. I, therefore, think that trying to reproduce the problem is going to be tricky so perhaps logging access is a good idea in terms of being able to pinpoint where it's going wrong?
SMCorderPAYPALRESP is a TEXT field so there should be no issues with data size for that field. I've included an example, privately below, of what is written to that field for successful transactions., fyi.
If you are able to add something to pp_confirm.php that can log access, I can let you know when a transaction fails again and we can take it from there.
Thank you Ray.