merging from the branch and conflicts impossible !!!

[Casper]

hi all,
I would like to ask for some help if possible!

I have this scenario with CVS:
- the trunk is the main development line
- the branch is the production released software

New dev occurrs on the trunk.
So lets say that I have file.txt both on trunk and branch and it
contains the rowss (will write the content of the file between two
lines):
-------------------------
numero 3
-------------------------

On the trunk I do some new dev and add some more stuff:
-------------------------
newdev
newdev numero 3 newdev
newdev
-------------------------


Meanwhile I apply a patch on the branch to resolve a bug, so the
file.txt on the branch is :
-------------------------
patch
patch numero 3 patch
patch
-------------------------


Once the patch is tested, I tag it "rel_3_0_1".

I have to copy it to the trunk as well, doing something like this, I
try a first merge, relove the conflicts manually and get the following:
-------------------------
newdev
patch
patch newdev numero 3 patch newdev
patch
newdev
-------------------------

I tag this as "merged-rel_3_0_1".


Now... again, I do some more dev on the trunk:
-------------------------
NEWDEV
patch
patch NEWDEV numero 3 patch NEWDEV
patch
NEWDEV

SECONDO NEW DEV
SECONDO NEW DEV
-------------------------

And apply one more patch on the branch:
-------------------------
secondaPatch
patch
patch numero 3 patch
patch
secondaPatch
secondaPatch
-------------------------

As you can see, here on the branch I only have patches, since I do not
copy the new dev code from the trunk to the branch... it must stay on
the trunk only.
Ok so, I tag the new patch as "rel_3_0_2".
And merge now:


Here's what I get:

-------------------------

secondaPatch
patch
patch numero 3 patch
patch
<<<<<<< file3.txt
NEWDEV

SECONDO NEW DEV
SECONDO NEW DEV

=======
secondaPatch
secondaPatch
>>>>>>> 1.1.1.1.2.3

-------------------------


The "NEWDEV" at line 1 and in line 3 HAS GONE !!!
Where is it ??!?!?
The problem is that when CVS does the merge it doesnt even write it in
the conflict so, how about that?
This file is pretty simple, but what if I have a big one with hundreds
of lines of code? I may miss it all !

I tried with a 3-way visual merge tool, and when it does automatic
merging, there's a conflict but it misses to merge NEWDEV as well !!!
and It does not signal it as a conflict.
I still can see it misses since it is visual, but how do I do with cvs
?

Any help please?
thank you very much