If you copy or move files arround or if you generate and delete variables the memory in your calculator gets fragmented. Locked memory blocks are normally blocks which are currently in use like the active program. Note that memory blocks which are located in the archive memory are also in memory-locked state. Each line in the Main View corresponds to a memory related handle. The displayed sizes are the sizes which are really allocated for a memory block.
Allocated blocks have always an even number of bytes.
So never assume that the value returned by HeapSize is the true number of bytes used by the data stored in the heap block. The header line contains the same data as the corresponding line in the Main View. If a handle cannot be found within the VAT this screen will only show a small note. This flag has nothing to do with the memory-locks. These lock only a logical lock which is used by the AMS when you lock a file using the Var-Link screen.