[OE-core] OE-core] How do I find out why are packages being rebuilt?

[Mike Looijmans]

I'm still having trouble with packages being needlessly rebuilt over and 
over. The worst of all it qt4-embedded, it takes about an hour to build. 
This is wasting a LOT of time.

The classic OE never rebuilt a package until its version changed.

How and why the current oe-core decides to rebuild package is a complete 
mystery to me, and the outdated documentation on the oe wiki isn't any 
help in that respect either.

Can anyone explain how I can gain some insight into the "trigger" that 
causes a certain package to be rebuilt?