high cpu usage when idle

If I leave nautilus open to my home folder or most any folder, it uses 25% of the cpu according to top. I've not had it open most of the time, but the cpu time is at 29:05 with a system up time of 17:30:21. That is more than twice the cpu time of Xorg and more than any other process in the system. I have deleted all bookmarks, just in case. If I navigate to a folder with only a single text document in it, the high cpu use stops.

Surely this must be a bug. What is it doing? If it is scanning something, shouldn't the results be cached and the scanning stop after a while? Does nautilus try to prefetch all folders recursively or something?

Also, all thumbnails in my Pictures folder show a clock or a black rectangle. In Ubuntu 14.04, I believe they showed thumbnail images. Could it be that it is trying a failing to load thumbnails?

Ubuntu 15.10 64 bit, fully updated
Nautilus 1:3.14.2-0ubunutu13

Running on Dell XPS 17
Memory: 15.6 GiB
Processor: Intel® Core™ i7-2670QM CPU @ 2.20GHz × 8
Graphics: GeForce GT 550M/PCIe/SSE2 (this is an Intel/Nvidia Hybrid setup running Nvidia binary driver 340.96 from nvidia-340-updates )
Drives: 2 SSDs (512 and 250GiB)

Fresh install but home partition copied from 14.04.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: nautilus 1:3.14.2-0ubuntu13
ProcVersionSignature: Ubuntu 4.2.0-34.39-generic 4.2.8-ckt4
Uname: Linux 4.2.0-34-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CurrentDesktop: Unity
Date: Sat Apr 2 17:24:04 2016
EcryptfsInUse: Yes
GsettingsChanges: b'org.gnome.nautilus.list-view' b'default-column-order' b"['name', 'size', 'type', 'date_modified', 'date_accessed', 'owner', 'group', 'permissions', 'mime_type', 'where']"
InstallationDate: Installed on 2016-03-22 (11 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
SourcePackage: nautilus
UpgradeStatus: No upgrade log present (probably fresh install)