Time Machine restore does not recognize sparsebundle password

I am trying to do a time machine system restore from an encrypted sparse bundle. I have a mac with OS X 10.10.2 and the sparse bundle is on a time capsule. I rebooted with cmd+R and selected “Restore from a Time Machine Backup”. I was asked for the time machine password and then selected the sparse bundle I wanted to restore. At that point I was asked for the sparse bundle password, which however the system keeps rejecting.

I am 100% sure the password is instead correct. To double check I restarted the mac and checked in the keychain, and the password is in fact correct. Also I could restore specific files from time machine without any problem. But when I try the system restore the way I just described, the system does not recognise that password as the correct one.

Can anybody suggest a solution? thanks