Default /system won't stay mounted as rw

Hello all,

I have been trying to gain root on a Android 4.0.4 device and was able to, but I can't seem to keep system rw long term.

I run the following command

mount -o remount,rw /system
or
adb remount (from a PC)

the mount command will then show that system is in rw mode. However, if I attempt to copy any data into /system, the first file copy fails and the system then reports read only. To make things even more odd, commands like chmod on a file in /system work just fine.

It seems to me that there is something that detects something writing to /system, and then forces the mount back to ro.

Does anyone have any ideas about this? Is this a common technique manufactures use?
The closest thing I could find on XDA is a reference to Sony Xperia devices having a watchdog service that doesn't something like this, but this device is a Kenwood Head unit and not a Sony device.

Thanks!