This is what I explained by PM to somebody, who asked if this was in fact true or not. I thought it was worthy of posting here.
This is at every Registrar, although there may be a few who ignore it and add the year. It's in the ICANN rules (somewhere). If you transfer a domain within 45 days of it being renewed, the receiving registrar will not add another year of renewal. Meaning you have paid twice and only received 1 renewal. You have to go back to the old Registrar to get your refund. You can easily miss this not adding another year because you automatically assume it's been added with the transfer. I only notice it at Dynadot because I'm always transferring domain to Dynadot. Some Registrars I've received a refund, some I haven't, and some I just never bothered to ask for a refund. I don't remember which ones do and which ones don't pay up. I've particularly noticed it with domains won at SnapNames. I like to transfer these ASAP to Dynadot. I believe also it is why eNom place an Auction Lock on domains won at NameJet.