I submitted this as a bug report, but here's my workaround for now. for me it happens primarily (probably only) with flexed regions. it seems to be related with tempo information in the clip either getting corrupted or read wrong.
I've made lots of attempts at correcting tempo info on files, erasing tempo info on files, etc etc but these not only dont reliably work, but its very time consuming. So for now, the only way to reliably work around this is to put a flex marker where i want to make the cut, and then make the cut. I never used to have to do this before 10.7 came out.