There is a bug in the LG KU250 firmware (at least as of software version 10d) that if you transfer a file with a long file name which is longer than that the phone supports the file simply disappears but the space is occupied from the common memory of the phone. (This problem may not occur if you used external MicroSD card.)
The only option appear to be to restore the firmware into default state. The reset function as well as clear all memory function doesn't solve the problem. A factory reset code wasn't available to be known at the time of writing.
Note: LG KU250 is The winning handset in the GSMA's "3G for All" program 2007.