The original papers describing the reaction:

http://pubs.acs.org/doi/abs/10.1021/bi00816a016

http://www.ncbi.nlm.nih.gov/pubmed/5495733

methylcytosine is actually converted to thymine, albeit at a much slower rate than that of cytidine conversion to uracil. A great paper from M. Ehrlich's group, comparing the conversion kinetics of these reactions in ssDNA:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC324387/