Memory reported as full without being full

I am having storage issues with my Samsung Galaxy S Duos. I solved it by moving apps from phone memory to the SD card, so now 1.2 GB of internal space is free. However, it still tells me that I have insufficient storage for apps. I found that there are 94 MB of cache files there, but even if that's the case I should still have plenty of free space. Why does my phone still think that the internal storage is full?