Where to look for render not shown

I have in Blender 2.71 a strange problem with building a Minion …
I save a new blend file at important steps done.
Normal render works in file 3 … adding more in 4 and 5
Only the last added mesh renders (not cycles) but the parts of what is built in 3 is not rendered.
In 4 I must have switched on something what triggers not showing earlier created meshes.

WHERE could be the reason ?

Luckily I solved the problem by starting at 3 and linking from 5 … but to know WHY … I got this is worthwhile for me
at least :wink:

Here again the problem is visible, the '“Brille” is copied by Shift D and placed on the right eye
but does not render?

I would look it from the attached .blend instead of listing possible causes.

you meant looking = linking ?

I would like the REASON why, bug or I do something I do not realize … ;-(

No, I meant that I would check the .blend if it was attached.