Despite checking the "Save password in your keychain" checkbox in the "Authenticate" dialog that shows:

Login required for: https://bitbucket.org

SourceTree asks me to authenticate each time I start it. After entering my bitbucket password I am able to access my bitbucket projects. Each time I authenticate in this way the Mac System Console shows the following error:

5/2/16 4:08:04.167 PM SourceTree[20439]: SecOSStatusWith error:[-34018] Error Domain=NSOSStatusErrorDomain Code=-34018 "client has neither application-identifier nor keychain-access-groups entitlements" UserInfo=

{NSDescription=client has neither application-identifier nor keychain-access-groups entitlements}