pause button only slows not pauses

To reproduce I used an usb3 external hard drive I was copying large files to in pcmanfm. 1. Open pcmanfm press the new tab button and in that tab navigate to your large file. Then in the first tab select the external hard drive on the first tab. Copy the large file and then paste it in the desired location on the external hard drive. A dialog explaining the time remaining should appear with two buttons that say stop and pause. Click the pause button. Notice the progress bar slowly inches forward even though it says resume but at a slower rate.

pcmanfm:
  Installed: 1.2.3-1
  Candidate: 1.2.3-1
  Version table:
 *** 1.2.3-1 0
        500 http://us.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status
Description: Ubuntu Vivid Vervet (development branch)
Release: 15.04
libfm4:
  Installed: 1.2.3-0ubuntu1
  Candidate: 1.2.3-0ubuntu1
  Version table:
 *** 1.2.3-0ubuntu1 0
        500 http://us.archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
        100 /var/lib/dpkg/status

information on extrenal drive from lsusb.
Bus 002 Device 002: ID 0bc2:2320 Seagate RSS LLC USB 3.0 bridge [Portable Expansion Drive]
  idVendor 0x0bc2 Seagate RSS LLC
  iManufacturer 2 Seagate

I expected the pause button to temporarily stop the transfer. Instead it continued at a slower pace. If it is intended to continue at a slower pace I am not sure pause is the correct label for the button and think there should be a better label but can't think of one right now.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: pcmanfm 1.2.3-1
ProcVersionSignature: Ubuntu 3.18.0-8.9-generic 3.18.1
Uname: Linux 3.18.0-8-generic x86_64
ApportVersion: 2.15.1-0ubuntu1
Architecture: amd64
Config_pcmanfm_System_Lubuntu: Error: [Errno 2] No such file or directory: '/etc/xdg/pcmanfm/Lubuntu/lubuntu.conf'
CurrentDesktop: LXDE
Date: Wed Jan 7 12:39:46 2015
InstallationDate: Installed on 2014-09-30 (98 days ago)
InstallationMedia: Lubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20140930)
SourcePackage: pcmanfm
Udisks_dump: Error: [Errno 2] No such file or directory: 'udisks'
UpgradeStatus: Upgraded to vivid on 2014-12-12 (25 days ago)