It claims svchost.exe "(LocalSystemNetworkRestricted)" is doing the reading of files, and the flurry of disk activity doesn't start until about 5 seconds after the app has been closed, and is off the applications/processes lists (with them updating at high speed).
All the random files are listed as 'background' IO priority - might it be prefetching or something? Why would it prefetch so much for that specific .cap and not others? I'm not doing anything weird with it.
Upon checking what's running, it claims PID 1064 is doing the reading of files - the services running under that are:
wudfsvc - Windows Driver Foundation - User-mode Driver Framework
WPDBusEnum - Portable Device Enumerator Service
WdiSystemHost - Diagnostic System Host
UxSms - Desktop Window Manager Session Manager
TrkWks - Distributed Link Tracking Client
TabletInputService - Tablet PC Input Service
SysMain - Superfetch
PcaSvc - Program Compatibility Assistant Service
Netman - Network Connections
hidserv - Human Interface Device Access
EMDMgmt - ReadyBoost
AudioEndpointBuilder - Windows Audio Endpoint Builder
That's a lot of stuff that I don't know what is. This is a new PC with little on it other than construct and a few graphics apps, and it's not hooked up to the internet.