Just as a side note to the other (good)good answers - developers tend to have minds that look at process and (un)consciously find ways to game it.
What you are training your developers to do here is to not raise tickets for defects they find when they are developing (as either they, or possibly worse for them, one of their colleagues) would then have to work late to fix it.
If it's a subtle bug, they may just hope nobody notices (particularly if it's not directly related to what they are doing at that point in time).
It's well known that the earlier you find a bug, the cheaper it is to fix - if this results in more bugs being found in live rather than during development cycles, then this can't be a good thing.