I did an importaddress on a node that was catching up to the chain:
2016-05-30 08:33:49 Still rescanning. At block 188494. Progress=0.017878
...
2016-05-30 09:09:49 Still rescanning. At block 410380. Progress=0.985130
2016-05-30 09:10:02 AddToWallet xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx new
2016-05-30 09:10:11 AddToWallet xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx new
2016-05-30 09:10:32 AddToWallet xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx new
2016-05-30 09:10:49 Still rescanning. At block 412520. Progress=0.993962
2016-05-30 09:11:13 UpdateTip: new best=00000000000000000178e16cbbd65a307731a25920e8c28d5e25ac7fa8eb187b height=412954 version=0x20000001 log2_work=84.705608 tx=130774826 date='2016-05-22 22:4
6:55' progress=0.995627 cache=8.1MiB(4642tx)
...
2016-05-30 09:14:11 UpdateTip: new best=0000000000000000058f6316dbad0e4d92d7251d82e14847ed72200abbc43613 height=412975 version=0x00000004 log2_work=84.706409 tx=130787669 date='2016-05-23 00:42:27' progress=0.995673 cache=136.5MiB(43679tx)
*****************HERE****************
2016-05-30 09:15:12 Still rescanning. At block 190269. Progress=0.019200
2016-05-30 09:16:12 Still rescanning. At block 214210. Progress=0.038713
2016-05-30 09:17:12 Still rescanning. At block 229009. Progress=0.056448
2016-05-30 09:18:12 Still rescanning. At block 244788. Progress=0.074901
2016-05-30 09:19:12 Still rescanning. At block 263481. Progress=0.093536
2016-05-30 09:20:12 Still rescanning. At block 277685. Progress=0.111176
2016-05-30 09:21:12 Still rescanning. At block 289438. Progress=0.126862
2016-05-30 09:22:12 Still rescanning. At block 299963. Progress=0.169717
At the *****************HERE**************** it looks like the rescan is interrupted and starts from scratch (or at least, block 190269). This is possibly caused by the blocks that were added to the tip in between.
(I was importing a multisig address, if that makes any difference)