Difficult Rashi

In Parshas Vayeishev [38/8] - Yehuda tells Onan to perform Yibum by marrying his brothers widow והקם זרע לאחיך - Rashi explains - the child will be named after your brother and you will thus establish seed for your brother. "הבן יקרא על שם המת".

Anybody who learns Yevamos [including the Ramban] and reads this Rashi, jumps out of his seat. The gemara [כ"ד] explicitly says that the child born from a yibum union is NOT named after the late brother. How can Rashi contradict an explicit gemara??

[Funny - as I was typing this, I heard a shiur in the background and the speaker said that when doing chalitza, the man takes off the woman's shoe. Hmmmmmm. The pasuk says וְחָלְצָה נַעֲלוֹ מֵעַל רַגְלוֹ, she takes off HIS shoe. Nobody's is perfect:-). But Rashi knew what he was talking about and requires a terutz].