you're using legacy X10 mouse reporting when you really want sgr.  add to your .vimrc:
  set ttymouse=sgr

i've posted a fix for X10 reporting, but haven't finished writing unittests.

set ttymouse=sgr

in addition to 

set mouse=a

in my .vimrc - disabling all other lines - does not lead to wanted behaviour for copying out of vim/hterm into (other) windows7 programs. FYI this is vim 7.4.273 modified by Gentoo-7.4.273

sorry, but i don't understand your issue then.  please describe precisely the steps you're taking and what you expect to happen.

i don't know what "<shift> <left mouse mark>" means.  you also say "in hterm" but then say "not through secure shell".

We are on a windows7 box.
Normal windows behaviour would be to <ctrl><c> Copy and <ctrl><v> Paste a text.

Putty (the ssh client for windows) works a bit different. Inside putty window you mark text holding the left mouse button down. You can then paste this text as above. This works for stuff you have typed onto the command line or that the machine gives back to you.

To have copy and paste for the Vi(m)-Editor, you first need to enable the mouse (set mouse=a). Otherwise no copying of the text. For putty you need to hold down the <shift> button while selecting text with your mouse. Then copy and paste works great out of vim on a putty ssh-terminal.

This does not work for the chrome browser plugin that has the same functionality as my putty (you call it hterm, is that correct?).

selecting text in hterm to automatically trigger a copy event should work fine in Windows today

what you're describing is enabling mouse mode, then temporarily disabling mouse mode so as to start a local selection for the purpose of copying.  putty allows that by holding down shift.  support for that is being tracked in issue 342944 if you want to star it.