It's usually worth a check over from a vet, jut to make sure there's nothing wrong physically.

I'm no expert, and I'm only parroting what I have read.

There is a good chance this is caused by stress. When you moved in, and everything seemed to settle down, there is a chance that the cat was unhappy right from the start, and that this soiling is only happening now as Tigger gets to the end of (his/her?) tether.

Cas don't exhibit stress in easily recognisable ways until tis kind of thing happens. This may be caused by a subtle change the relationships between the cats that was brought on by the move, or it might be caused because of the presence of new housemates in general, and the fact that the cat has been moved.

If it persists, then it might be worth asking for a referral to a behaviourist. At the very least, I'd suggest reading Cat Confidential or Cat Detective by Vicky Halls: very cheap on amazon, and probably also available at the library.