Z80 CPU bugs?

Hello List, I've been developing my own Z80 SBC kit computer (who hasn't?) and have been debugging CP/M 3 on it. I seem to have come across an interesting problem with the LDIR instruction which appears on some 10MHz Z80 CPU's I bought from Farnell, but not on what are probably Chinese fakes which are supposed to be 20MHz. I'm running the system at 6.75MHz. The problem is when I execute the LDIR instruction, it writes an additional zero to memory. Say if I transfer 16 bytes, it'll transfer them correctly but overwrite the 17th address with a zero. Does anyone know anything about this? I've looked for a list of revisions or bug fixes from Zilog but haven't come up with anything. The Z80's in question are marked: zilog Z84C0010PEG Z80 CPU 1209 Thanks, Alexis K.