Hey Ilan - I did the test with Singularity ... behaves the same as Firestorm!
Meanwhile I tested more: it happens also when I login directly with the viewer to last visited place ( not only when I click the enter button of the web-page before).
What is different from one day to the other? It's most obviously happening mostly (but with exceptions) at the first login of a new day!
It also affects not all attached objects : affects nearly allways the mesh boots , at 90% of occasions the hair (which is not mesh) fully or in parts , usually not affecting the arm - or ear-rings.
Can it be related to the way how items are arranged in multiple outfits?