The array's returned by getMulti() are not correctly keyed or are in some other way broken. When one tries to reference the key via it's name, an "undefined index" error is returned. array_key_exists() also returns false.
This paste has some sample code:
Both the top and bottom cases should end in bool(true).
avsej mentioned in IRC that these two portions of code should be compared:
Thanks for digging into this issue.