For some reason whenever I try to move a file to my internal system through root explorer, it keeps failing lol.. I am only moving an 8mb BootAnimation to replace the current Oppo boot animation so I am pretty sure that I have enough space.
I also struggled over that after rooting my device.
phps it is a bug in android 4.3.
I managed to copy stuff to internal storage with "ES Datei Explorer" - ES File Explorer - I hope it helps.