Piston 1.4.0 import will set the revision to that of the head and not that of the last changed revision. A piston update
after an import will properly set this.

Example in a Rails project if you do a:

 piston import http://mabs29.googlecode.com/svn/trunk/plugins/simple_sidebar/ vendor/plugins/simple_sidebar

It states: 

"Exported r51 from 'http://mabs29.googlecode.com/svn/trunk/plugins/simple_sidebar/ ' to
'vendor/plugins/simple_sidebar'"

Preforming a piston update sets the proper last changed revision:

Processing 'vendor/plugins/simple_sidebar/'...
  Fetching remote repository's latest revision and UUID
  Restoring remote repository to known state at r51
  Updating remote repository to r2
  Processing adds/deletes
  Merging local changes back in
  Removing temporary files / folders
  Updating Piston properties
  Updated to r2 (0 changes)

I'm going to see about working on a patch and submitting it.