You can see this in your example as the first two records start at address 0x0000 and 0x0003 and each contain the 3 bytes that go into the reset and first interrupt vector.

Because compilers often generate hex files with minimal amount of data in it, i.e., they only write the data they need to write, other memory locations will be whatever they were before you loaded your hex file. If you are using a checksum as any kind of indicator that you've loaded the code properly, you will need to write FF's to your buffer before loading the hex file. Otherwise your checksum will depend on whatever code was loaded previously.

My programmer maintains its buffer between uses, so filling it with FF prior to loading the hex file is now my standard practice.

I don't suppose your verify procedure uses checksums?

Dennis