It is cross-talk that affects the jps of the second pants.  The pants probably have JPs that just barely fill the bill.  When a second pair of pants comes in, it just barely doesn't work.  I've run into it lots of times.  Just adjust the JPs with the Joint Parameter Window, and you're good to go.

I cannot save the world. Only my little piece of it. If we all act together, we can save the world.--Nelson Mandela
An  inconsistent hobgoblin is the fool of little minds
Taking "Just do it" to a whole new level!