[O] Bug: dragging a line in agenda moves following hidden lines

[Thomas Morgan]

Hi, Org mode hackers,

There seems to be a bug whereby dragging a line pulls along adjacent
hidden lines.

I'm using Org-mode version 8.2.5g (`release_8.2.5g-663-g24a213' @
`/src/org-mode/lisp/') and GNU Emacs 24.3.1 (`x86_64-unknown-linux-gnu',
X toolkit, Xaw3d scroll bars) of 2013-09-24.

I started Emacs with `emacs -Q -l setup.el' (file attached).
This opened a day agenda view.

,----
| Day-agenda (W05):
| Sunday      2 February 2014
|   test-case:  Scheduled:  TODO Pick up package from post office        
:errands:
|   test-case:  Scheduled:  TODO Clean stovetop
|   test-case:  Scheduled:  TODO Buy water at store                      
:errands:
`----

I typed `/ TAB errands RET' to restrict it to items with the tag
`errands'.  The restricted view looked like this:

,----
| Day-agenda (W05):
| Sunday      2 February 2014
|   test-case:  Scheduled:  TODO Pick up package from post office        
:errands:
|   test-case:  Scheduled:  TODO Buy water at store                      
:errands:
`----

I moved point to the line containing "Pick up package" and typed
`M-<down>' to drag the line forward.

,----
| Day-agenda (W05):
| Sunday      2 February 2014
|   test-case:  Scheduled:  TODO Buy water at store                      
:errands:
|   test-case:  Scheduled:  TODO Pick up package from post office        
:errands:
`----

Then I typed `/ /' to remove the tag filter.

I expected that the hidden line, "Clean stovetop", would remain
in its position above "Buy water at store", like this:

,----
| Day-agenda (W05):
| Sunday      2 February 2014
|   test-case:  Scheduled:  TODO Clean stovetop
|   test-case:  Scheduled:  TODO Buy water at store                      
:errands:
|   test-case:  Scheduled:  TODO Pick up package from post office        
:errands:
`----

But in fact "Clean stovetop" had been dragged under "Buy water at store"
along with "Pick up package".

,----
| Day-agenda (W05):
| Sunday      2 February 2014
|   test-case:  Scheduled:  TODO Buy water at store                      
:errands:
|   test-case:  Scheduled:  TODO Pick up package from post office        
:errands:
|   test-case:  Scheduled:  TODO Clean stovetop
`----

I think it would be more useful and intuitive for hidden lines not to be
affected by dragging.

Thanks,
Thomas