The randomness has probably gotten worse since the TW kernel was changed to load sd-mod as a module. For straight forward desktops, the previous level of stability can be restored, see Bug 1216070 - Assignment of /dev/sd* has altered dramatically comment #33 for a fix which is in the process of delivered in TW.
For Leap there see comment #29 of the same bug report.
There was also a forum thread on the topic