In gene annotation table/gff3, why is same gene name appeared in different chromosome
 

I found some genes with same gene name but in different chromosome, anyone knows the reason?
For example:
chr19 hg18_refFlat gene 763518 772952 . - . ID=PRG2;
chr11 hg18_refFlat gene 56911410 56914706 . - . ID=PRG2;

chr8 hg18_refFlat gene 38576850 38577932 . - . ID=RNF5P1;
chr6 hg18_refFlat gene 32254210 32256545 . + . ID=RNF5P1;

chr24 hg18_refFlat gene 1670486 1681411 . + . ID=SFRS17A;
chr23 hg18_refFlat gene 1670486 1681411 . + . ID=SFRS17A;

Does anyone tell me where I can find related introduction about this kind of problem? Thanks a lot!

Aren't chr23 and chr24 chrX and chrY ? I am facing a similar problem with some illumina data.