I feel bad spending so much time on this situation. I I understood my problem coming effectively from an out of gas issue.
What I didn't know was that the gas to be used was not taken by default from the constructor gas field. I now understand that the javascriptJavaScript function of the instance should be passed a {from: account, gas: '}{from: account, gas: <gas to use>}
each and every time.
This is annoying considering that the remaining gas will be returned to the account caller.
Is there a way to set by default the gas to be sent in the same way we have the eth.defaultAccounteth.defaultAccount
?