Days and days to even work out why plugin settings weren't being set correctly and getting no-where, then this morning, within a couple of minutes of loading the project... it's fixed!
The issue was when a Profile was set, the Profile's active Method ("a method of sorting files") wasn't being initialised (which, among other things, passes the relevant settings on to the plugin). This doesn't make much sense as that's something that must have been happening previously otherwise it wouldn't work in the past. Was it broken all this time? Nineteen releases and no-one's mentioned it? Even I didn't realise?
That can't be right.
But, it's fixed, and I've created a new build and sent it to the user mentioned in previous posts to see if his original issues are fixed. If they are, then it'll be time to release 4.20 - a release all FileSieve users should update to.
Wondering if I should take a little break until I get the go ahead or if I should move this development blog over to the main domain...