When I wrote the last message I forgot to specify the following:

This morning Amanda reported the last backup on Tape2, and then asked for "a 
new tape" only, instead of "Tape3 or a new tape".
I put Tape3 in the unit anyway and amcheck stopped complaining for the wrong 
tape. Amanda is going to use Tape3 for the next backup (which is just the 
correct behavior).

This suggest me that amcheck DOES KNOW that Tape3 is the correct tape for the 
next run, BUT, for some reason, doesn't tell me.

BTW, it's Amanda 2.4.3 on RH9

What am I missing?