/sd-ext gets suddenly remounted read only during work

I have an HTC Desire with cyanogenmod 7.2 (with pdroid patch) and with an partitioned microSD card (first: FAT, second: ext3). The second partition gets automatically mounted read/writeable as /sd-ext as it should be. I'm using S2E to store my apps and the app data on this ext3 partition. The mount command shows me that the ext3 partition is not only mounted to /sd-ext but also to /data/app and /data/data. All of them are mounted read/writeable. My first question: Is it normal and secure that multiple directories are bound to the same partition? Are there no conflicts? In the beginning everything worked fine. I could install and use my apps without problems. But after a while more and more apps begun to crash and I always had to restart my phone to get rid of those crashes again. I discovered that the crashes where caused by a read only data partition. In fact all the directories /sd-ext, /data/data, and /data/apps where suddenly mounted read only. My second question: Why does Android sometimes remount my ext3 partition in read only mode while I work with my phone?