If I sort of summarize my take on it...
Some narrative conventions become so overused, exaggerated, and/or shorthanded that they fail to have any bearing on why the concept was entertaining to begin with. If they hang around anyway, the trope turns into dull filler that is only still used on merit of tradition. A deconstruction attempts to get back to the roots of why a convention was entertaining when it originally caught on, or tries to compare it to new but related elements to make it interesting again.
And yet this act of chipping everything apart and juxtaposing it with new ideas can wear out its welcome too, and the attempt to get back to a more direct execution would be called a reconstruction.
In the end, I think the two end up meaning almost the same thing at a glance. It's simply an attempt to make a standing convention more engaging after it's worn down its value.
The difference usually relies on the way the trope is messed with: if it is thoroughly explored, picked apart, and recombined with other ideas over the course of the story, then it's a deconstruction; if its being played in a straightforward way that the audience will easily recognize, it's a reconstruction. Then again, even this distinction feels a little arbitrary and out of place in certain stories. And for either term to work, it had to grow into a trope to begin with, so being an original trend setter would be plain old 'construction'.
Anyways, even an arbitrary definition is pretty important from where I see it. The word 'deconstruction' is kind of like 'egregious,' or 'trite,' with a lot of its meaning being dependent on the context. So it often gets thrown into places where a full description probably could have been more concise, if admittedly more cumbersome. The word catches on as the method of deconstructing/reconstructing things becomes popular, until it becomes the phrase you slap in your blurb to sound relevant and intellectual. Since the meaning is subtle and not universally applicable, people inevitably end up misusing it (and then ironically, a new word that can be used similarly, but hasn't been bastardized into oblivion catches on, deconstructing everyone's vocabulary...).
Still, while many stories aren't conducive to the two terms, I don't think they're always unnecessarily simplistic. As long as you don't demand an absolute formula that must apply to every narrative, these definitions end up doing their job well enough to support some useful discussion and analysis.