I'm using 5.6 and noticed similar ssh problems.
Setting up a rb750GL which comes with 5.2ish, I can not use SCP to update the firmware. Have to use FTP. This is regardless of wheter admin has a password assigned yet.
Updated to 5.6 and see the SSH problems discussed here. I don't use the older version, so I can't know for 5.5 or 5.2.
I also put it on a 433ah and see similar.
ssh with keys works and disables ssh access from that host. This isn't a feature. It should only disable access from a user at that host if it were a feature. All users at the remote host can't get in with a password after setting up a key on the MT. keys are for individual accounts on a host, not for the whole host and not for other hosts connecting to admin.
Here's an example where I setup a key on the MT to accept passwordless admin connections from my jp@huehuetenango account. After setting this up, I can not ssh in as admin from anywhere except that username on that host. Other accounts on the same machine also can not connect. Telnet, winbox, ftp, are not affected.
ptyler@huehuetenango:~> ssh admin@69.39.112.241
admin@69.39.112.241's password:
Permission denied, please try again.
admin@69.39.112.241's password:
Permission denied, please try again.
admin@69.39.112.241's password:
Permission denied (password).
ptyler@huehuetenango:~> exit
logout
huehuetenango:~ # exit
logout
jp@huehuetenango:~> ssh admin@69.39.112.241
MMM MMM KKK TTTTTTTTTTT KKK
MMMM MMMM KKK TTTTTTTTTTT KKK
MMM MMMM MMM III KKK KKK RRRRRR OOOOOO TTT III KKK KKK
MMM MM MMM III KKKKK RRR RRR OOO OOO TTT III KKKKK
MMM MMM III KKK KKK RRRRRR OOO OOO TTT III KKK KKK
MMM MMM III KKK KKK RRR RRR OOOOOO TTT III KKK KKK
MikroTik RouterOS 5.6 (c) 1999-2011 http://www.mikrotik.com/
Property of Midcoast Internet Solutions 2075948277 or www.midcoast.com
Unauthorized access will be prosecuted.
All Access is logged.
[admin@squirrelap] > quit
interrupted
Connection to 69.39.112.241 closed.
jp@huehuetenango:~> exit
logout
Connection to 10.0.0.7 closed.
jp@travelmug:~> ssh admin@69.39.112.241
admin@69.39.112.241's password:
Permission denied, please try again.
admin@69.39.112.241's password:
Permission denied, please try again.
admin@69.39.112.241's password:
Permission denied (password).
jp@travelmug:~>
It is also worth mentioning as others have that using keys should not prevent password access; thats the way the old 4.x and 3.x routerOS works.
I use keys for automated access (backups locking and unlocking customers, things you can't do with snmp, etc...) and password access ssh is used for interactive staff use.
Also a bug related to this is that it does not log these failed ssh access attempts. This last problem inclines my mind to think it's not a feature.