Problem with recognize IDE secundary (LTR and LTD)

Hello, I have installed in primary IDE two HD, and in secondary IDE, I installed Liteon LTR-48125W (master) and Liteon LTD-163 (slave).
When I run PC, recognize
HDD Ide primary master…xxHD1xx
HDD Ide primary slave …xxHD2xx
Found CD-ROM… xxxLTRxxx
Found CD-ROM… xxxLTDxxx

Because not detect HDD seconday IDE master and slave for optical units?
Today, I desconect LITEON LTR, and then, PC recognize DVD LTD in secondary IDE slave, but if I connect two optical units, the pc recognize with CD-ROM.
The LTR that I desconect, I installed in other PC, and this PC recognize also how “Found CD-ROM”
Because ensue this? I haven´t problem with run, but I want know because ensue this.
Do you help me?