The effect of this seems to be easiest to reproduce by having a larger inventory, mine is 155K+. For me it reproduces on two different computers, running either Firestorm or the SL Viewer.
  1. Log in, open an inventory window (Ctrl + I)
  2. Open Windows' Task Manager, monitor your RAM usage
  3. Open a bunch of extra inventory windows, a few at a time (5, 10, 15, 20) (Ctrl + Shift + I)
  4. See how RAM usage increase, and if you just let it be, the RAM usage continues to go up for some time...
I don't know how common it is to have a bunch of inventory windows open at once, but it would seem to me that there might be room for optimization here, with all the windows not having unique data but are views into the same data I think that it shouldn't be duplicating the data in RAM for each window like it seems to do???