The sorting behavior won't, to my knowledge, occur until the record is committed or until the client registers as "idle" with the server. It sounds like there's a triggerered script firing somewhere that's committing the record. Check the layout and see if there are any script triggers attached to any of the fields.
Thanks for your response. Yes, there is a script trigger on one of the fields that is committing the record so some calculated totals would refresh right away. Thanks so much for your response. I removed that script trigger and now the user stays on the record until finished. Sweet! They can live with the calculation total appearing a bit later. This has been driving me nuts. I have script triggers on all the fields, but only that one had a "Commit Record" component.
I believe in Filemaker 12 you can turn off Auto-resorting for at least the main list view. Not sure if there is an option for portals. But it looks like you worked around the portal issue. I've been bumping into this myself lately.