sororities stealing things from fraternities

[anon_sorority]

I'm currently having a problem with my chapter and I was wondering if anyone could give me some advice on what to do.

Some girls from my chapter of my sorority has a tendency to take objects from fraternity houses without their knowledge and store them in our house. At first it seemed harmless, and most of the objects were small things that belonged to individual members and were returned the next day, but I'm starting to become concerned about it. Some of the things that girls from my chapter are now taking are very significant to the fraternities (flags, composites and most recently, a charter) and sometimes do not get returned. Nobody in my chapter seems the slightest bit concerned about it, and our president has even participated in it. I'm not really sure what to do about it. I know my chapter would be very upset if someone took our composites or our charter, and yet they tell me that I shouldn't tell the fraternities where their things are because "they should have been more careful".

Does anyone else think this is a serious problem? Do other chapters do this? I really don't think our national office would approve and some of the fraternities are getting really mad at us.