The $path used by ":!start cmd" is different from my system $path in windows

Question

So I do a lot of python work in GVim on Windows 7, and I'm running into an annoying roadblock. This might be more of a Windows question, but it's happening in Vim, so ...

I have this in my python.vim file to quickly run the current file in python:

nnoremap <silent> <F5> :!start cmd /c "python %:p" & pause<CR><CR>

and I'm working on a python script that calls ImageMagick via the shell. So, I hit F5, and I get an error that ImageMagick is "not recognized as an internal or external command".

However, when I run the python file from outside of GVim, it performs perfectly.

Eventually, I ran :!start cmd, and printed the Windows %PATH% from that command prompt. Much to my chagrin, the ImageMagick folder was not on my path. However, :echo $PATH from within vim has it, the path is correct in my System Properties -> Environment Variables, and any other command prompt has it.

[edit] Per request, these are the different paths:

Start cmd path (the bad one):

Path=C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Python27;C:\Program Files\Common Files\Autodesk Shared\;C:\Program Files (x86)\Common Files\Autodesk Shared\;C:\Program Files (x86)\Common Files\Softimage;C:\Program Files\Common Files\Softimage;C:\Program Files\Intel\DMIX;C:\PROGRA~2\ALPSER~1;C:\PROGRA~2\ALPSER~1\(x86);C:\Program Files (x86)\QuickTime\QTSystem\;C:\Program Files (x86)\WinMerge;c:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\;c:\Program Files\Microsoft SQL Server\100\Tools\Binn\;c:\Program Files\Microsoft SQL Server\100\DTS\Binn\;C:\Program Files\Microsoft Windows Performance Toolkit\;C:\Python27\Scripts;C:\Program Files\TortoiseSVN\bin;C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\;C:\Program Files\Microsoft SQL Server\110\Tools\Binn\;C:\Program Files (x86)\Microsoft SDKs\TypeScript\1.0\;C:\Program Files\Microsoft SQL Server\120\Tools\Binn\;C:\Program Files\doxygen\bin;C:\Program Files\Microsoft DNX\Dnvm\;C:\ProgramData\chocolatey\bin;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files (x86)\Graphviz2.38\bin;C:\Program Files\Git\cmd;C:\Program Files (x86)\Vim\vim74 

Regular path (the good one):

Path=C:\Program Files\ImageMagick-6.9.0-Q16;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Python27;C:\Program Files\Common Files\Autodesk Shared\;C:\Program Files (x86)\Common Files\Autodesk Shared\;C:\Program Files (x86)\Common Files\Softimage;C:\Program Files\Common Files\Softimage;C:\Program Files\Intel\DMIX;C:\PROGRA~2\ALPSER~1;C:\PROGRA~2\ALPSER~1\(x86);C:\Program Files (x86)\QuickTime\QTSystem\;C:\Program Files (x86)\WinMerge;c:\Program Files (x86)\Microsoft SQL Server\100\Tools\Binn\;c:\Program Files\Microsoft SQL Server\100\Tools\Binn\;c:\Program Files\Microsoft SQL Server\100\DTS\Binn\;C:\Program Files\Microsoft Windows Performance Toolkit\;C:\Python27\Scripts;C:\Program Files (x86)\Autodesk\Backburner\;C:\Program Files\TortoiseSVN\bin;C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\;C:\Program Files\Microsoft SQL Server\110\Tools\Binn\;C:\Program Files (x86)\Microsoft SDKs\TypeScript\1.0\;C:\Program Files\Microsoft SQL Server\120\Tools\Binn\;C:\Program Files\doxygen\bin;C:\Program Files\Microsoft DNX\Dnvm\;C:\ProgramData\chocolatey\bin;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Program Files (x86)\Graphviz2.38\bin;C:\Program Files\Git\cmd;C:\Program Files (x86)\CMake\bin;

Does anybody have an idea where this difference is coming from?