[galaxy-user] CpG Masking changing alignment length?

Hi All, I have a general question about CpG masking. I have a .maf file, when I use the maf to fasta tool, it gives me an alignment of 2,735,329 bp. But if I CpG mask the .maf file (restricted definition) then I use the maf to fasta tool, I get a very different alignment length, 5,572,544 bp. It would be great to know what is the cause of these differences. THANKS! Mike