Defect is deferred in following cases as per my knowledge
1.when developer is not accepted the defect and at the same
time defect is valid..some contradiction occurs
2.When scope of the CR is tested but tester thinks that this
defect is also critical. So it comes as an enhancement.
3.When developer is delaying to give fix because some more
changes has to be done in the s/w

A defect is said to be differed because; The fixing of the 
defect is getting post pone because of some reasons like;

> The dev team is expecting few changes from the client
> Or due to some constarints the Dev is telling that they 
can't fix this defect is this release.

I hope 2nd and 3 rd points are matching with ur answer.

Some times a bug has no importance due to change in design. 
so this need to avoided .its termed as Deffered status

Deffer it is a defect Developers will fix in next build

The bug, changed to deferred state means the bug is 
expected to be fixed in next releases. The reasons for 
changing the bug to this state have many factors. Some of 
them are priority of the bug may be low, lack of time for 
the release or the bug may not have major effect on the 
software.