[TYPO3-mvc] 1.4 property mapping fails with empty relations?

[Tim Schoch | GSTALTIG]

Hello List

We've just updated from 1.3 to 1.4 and are having some troubles here.
In 1.3 we had used select fields for 1:m relations to other domain objects. Passing an empty value (or -1 in some cases)
should result in an empty relation. Without any changes to the source in 1.4 the exception #1297759968 «Object with identity
 "-1" not found» is thrown.

I've tracked the problem down to Tx_Extbase_Property_TypeConverter_PersistentObjectConverter::fetchObjectFromPersistence()
where empty objects allways throw an exception - even if the domain property isn't mandatory. ( -> @validate NotEmpty is NOT set )

Is this a bug or did I misunderstand something?
And how can we solve this, if its the new intended behaviour. My first guess would be a custom TypeConverter, right?

Cheers
Tim

ps: THANK YOU for extbase & fluid - I like it and would never want to go back to pi