[TYPO3-mvc] Persitence layer logic, execute()->getQuery()

[ktt]

Hello,

While updating extbase 1.2 to 1.3.1-devel I noticed that 
some cases of "...$query->execute();" in repository doesn't work
and give errors, change to "...$query->execute()->getQuery();" helped.
(this is documented in 1.3.0 Beta 1a changelog).
But some of "...$query->execute();" still work unupdated.
Is it possible to read more on Lazy loading and persistence layer
and explore the queries? It seems there are not much detailed
documentation about persitence layers online.

Thank you in advance,
Kast