404 in extended loop, something new since 3.0?

Something has changed since 3.0-3.04 that has disabled a custom plugin I wrote for importing MLS listings from a central database. The loop at its simplest;

– Retrieves a predetermined list of regions to import from.
– Queries the MLS database and returns an array of each region, one by one.
– Creates a post for each listing, and appends meta information and custom taxonomies to each.

It runs two primary loops, the overall loop cycles through each region, the seconday loop cycles through each listing for that region.

The import process can be rather length and as such is triggered via an asynchronous request and run in the background. I can also trigger it via a direct access when I disable certain security checks at the code level.

I’ve added a 100+ lines of debugging code to step through the loop piece by piece. No particular piece of the loop is kicking me out, but WordPress is arbitrarily decided after some as of yet unspecified length of time to kick me out of the loop and return 404 headers and the corresponding 404 page. It’s full on redirecting, as I lose all the debug info I send to stdout.

The changelogs have been no help to me, as I haven’t seen anything that remotely sounds like an alteration to this system that would cause the loop to fail at a specified time limit.

Any ideas where I can continue my search?