Hello,
I'm on Kubuntu, I have connections that's OK, but when I add a connection, it disappears restart disable !
What should I do to keep it ?
Please take some time and describe your issue with a few more details. I think its not really clear what issue you're facing.
I installed owncloud-client. I have 3 cloud accounts. The three accounts work, I can connect with owncloud-client. But for the latter, with each restart, the account is kept in owncloud-client.
Yes, with is the expected behavior. Why do you think that the sync client should not keep previous configured accounts / connections? This is one of these rare use cases which are very unlikely supported and never will get into the sync client.
It is a mistake, I mean that the account is not kept in owncloud-client
Ahhh, then its more clear 
If that is the case please create a new bugreport at: