OK, so looking some more, I think I finally hit on the right search phrase, or looked while under the right phase of the moon, and it seems that the LL viewers are not the only ones with the problem, and it has at least been assigned.
If you're a clothing creator or wearer of pants (I think that pretty much means everybody) you may want to have a look at this JIRA issue https://jira.secondlife.com/browse/ECC-49 Maybe a good one to go vote on - since it efects everyone in one way or another.
Even if you don't see the pants messed up on your viewer, know that there are a lot of people out there that are seeing you looking a lot different than you intended. If you wear pants that have a low rolled cuff, people see you in tights with a donut around your ankle. Not cool.
In the meantime, I will have to restrict my buying to pants with full prim lower legs - or wear a kilt.