Is "right-click > archive" unreliable?

[hermanaa]

Is "right-click > archive" UNreliable?

Properties original file:
/home/n0jn/.evolution
2830 items, totalling 732.4 MB
---
Properties tar.gz file:
/home/n0jn/.evolution.tar.gz
tar archive (gzip-compressed)
71.6 MB (75091898 bytes)  <this backup is NOT complete.
There was NO error-message.

I closed the program, Evolution, before making this tar.gz file.
---

I am checking because on I got stung previously. Similar problem,
unrelated backup, same procedure.

I will COPY the orig folder to my backup folder, make a tar.gz file
there. See how that works out.
(I discard the faulty 71.6 MB tar.gz file.)
Result (of the copying) using 'Properties' :
Orig dir: 2830 items, totalling 732.4 MB
Copied dir: 2830 items, totalling 732.5 MB

I dont like the 0.1MB difference. (ignore for now)
Check fs: /dev/hda2 on /mnt/G15B type ext3 (rw)
Source and destination of the copied dir are on the
 same partition, same fs.

I now archive the copied file:
(after renaming to: 081222.evolution)
Source: 081222.evolution. Properties: 2830 items, totalling 732.5 MB
Archive: 081222.evolution.tar.gz. Properties: 236.0 MB (247462734 bytes)
Observation: It took MUCH longer to make this tar.gz archive
(about 8x as long, compared to the 71.6 MB arch)

I am confident I have a good tar.gz now. (smile)
(I am changing my backup procedure).

Question: Why is my simple "right-click > archive" UNreliable?
(The program that uses the folder, Evolution, was NOT running).
I checked the user-named mail-folders: No unusual chars have been used.
Names with a space in it are common.

FYI:
I am the OP of: Stuck at 6.06LTS and no flashplayer.
(big Thanks for helping on that one, I will be back).
I need a good back-up, so I can take risks. (like: losing my 6.06LTS).
I changed my backup procedure after these tests. I think
 I got the problem licked.
But why "right-click > archive" does not do what is expected?

HermanPHL/ hermanaa.