apt warnings about missing public keys

After running apt-get update on a typically-stable mixed etch/sid machine (which also has experimental in the sources list), i'm getting the following warnings from apt:

W: There are no public key available for the following key IDs:A70DAF536070D3A1W: There are no public key available for the following key IDs:A70DAF536070D3A1W: There are no public key available for the following key IDs:A70DAF536070D3A1W: You may want to run apt-get update to correct these problems

Is anyone else seeing this? a quick glance at google makes me think it's not very important, but i'd like some confirmation on this. Also, the identical repeated error messages look odd. If it's one from each upstream source, shouldn't apt include the message about which source is generating the error? otherwise, why bother printing the same thing 3 times?