Hans Perk reminds me that The Plight of the Bumble Bee "mystery" had already been solved by him, Amid and Jerry from CartoonBrew a few months ago (how could I forget that?). You can check this link to find out more. Amid had mentioned at the time:

[There is a wealth of material in the Disney vaults and archives, developed and produced under Walt's watch, which never made their way to completion. The two in particular I'm thinking of are Mickey Mouse shorts: The Talking Dog and Plight of the Bumble Bee. Both were shelved late in their respective production schedules, in the early-1950s. Both have existing dialogue and music tracks, storyboards and were 98% animated (by the likes of Freddy Moore!). Two new classic shorts—just sitting there, simply waiting for ink-and-paint!]

So my next question is: does anyone one of you have more information about which artists were involved in The Talking Dog project and what the plot line of that short was?