I'm a male, I have a female roommate for over two years.
It should be noted right from the start that we have extremely smooth relationship - we literally never fight, argue or have any issues what-so-ever. She has her own life, I have mine. The only thing thats differs us from typical roommates is that we had tiny fling long long time ago.
About a year ago I have noticed that some items of mine begun to disappear - nothing especially important or of any monetary value - small things like postcards, pictures, small gadgets etc.
10 months ago, by chance, I discovered two items that I was missing ( packages containing $5 items i purchased online) in her car's trunk. When confronted, she said she picked it up from the mailbox on a way to her car and forgot about it. The packages were opened, however. I wasn't overwhelmingly satisfied with her lengthly explanation, but since the items in question were of marginal value and importance, I didn't make a big deal about it. I thought it was one-time weirdness over trivial stuff.
She assured me that this will never repeat itself.
But things continued to vanish. I didn't say anything though because i had no proof she took it. I'm absent-minded - there was a possibility I misplaced them.
A week ago, when she wasn't home , I saw a key next to her portable safe.
I don't know why I opened it, because it's decisively unethical, but I had a strong 'hunch'.
Inside, I found a heaps of my things - friend's postcards that I never received; regular snapshot photographs of me with my friends, my gf, my mother ..that I was missing ; my keys that I thought I lost; greeting cards from my gf and 4-5 other items of no significant sentimental or financial value.
Is this small steady mischief? (she's a very good person, though, always willing to help)
Is this some sort of feminine resentment manifesting itself ?
Is this some sort of mild psychological disorder?
Is this kleptomania? ( along with my things I found items belonging to unknown persons - like driver's license of some strange girl etc)
It might be kleptomania, as the things have no economic value. Confront her and encourage her to see a psychotherapist. Do not give her the opportunity to steal your things again. Lock them in to help her resist her urge to steal.