I have never heard of this happening but recently, something along these lines is taking place in a line of Afwreck clones that me and my friends have been growing for years. Over the last three years I have personally grown dozens of these plants and seen hundreds more grown both indoors and out. These are all the same "cut" of Afwreck - all these clones come from the same mother (or clones of that same mother). The last two runs we've done on the indoor and the last outdoor run started exhibiting wierd traits never seen before - like "fingers" growing from the tops of finished buds (I think some people call them King's Crowns), as well as a loss of density in all the big tops. I could be wrong but as far as we can tell, no other factors have changed. If every time we cut clones, we called it a new "generation", the clones we're growing now would be like the 30th generation. It appears as though this "generation" of clones is starting to "degrade". By this I mean that all the desirable traits that we chose to clone for have been disapearing slowly and all kinds of wierd things are happening. Crazy stuff.
P.S. I have no scientific evidence of any of this, its just based on my observations after growing the same strain a long time. It could very easily be something I/we are doing wrong and/or differently than we used to and are simply overlooking something. Or it could be that we smoke stupid amounts of hash and we are just bored of growing Afwreck