I made a raspberry melomel a month back and I came to bottling it, to notice this yeasty aftertaste. This is something I have experienced in my meads from time to time.
Before bottling I noticed that it was still bubbling after a brief period of stabalising. I racked it off and added sulphite (I can only get sodium), so I leave it for a while (possibly another month after back sweetening and stabalising) and I just opened a bottle of it and it tastes fine, a bit of an alcohol bite (it is young and I have a cold so my palate isn't the best) but there is this yeasty aftertaste to it. Could it be infected? If so, would I have to get rid of it? One thing that is never answered properly is what an oxidised mead tastes like, I have researched to no avail on the matter. I did notice some yeast fall from the surface when I racked it the first time as well (there were no yeast rafts on the surface).
There are no stupid questions - long winded or otherwise. The only stupid questions are the ones we don't ask.
I may be wrong but I wonder if you may be bottling before all the yeast has flocculated and dropped out of suspension and hence you taste the yeast. Are you saying that you are bottling a month after you pitched the yeast? That's when most mead makers view the most active part of the fermentation to be over and so there would be many months of aging and racking still to go. Is the yeast you are using a high flocculating yeast or does it tend to remain in suspension for a long time?
Did you use K-Sorbate when you stabilized? If not, you may be getting a fermentation restart. Sulphite alone will not prevent re-fermentation.
What was your final gravity? If was greater than 1.000, it is likely that you had residual sugar left to provide a source of food for the yeast, especially if the temperature increased. Often a final gravity as low as 0.996 can be reached before all of the sugar is used up.
The bubbling could be CO2 leaving the mead. Did you de-gas your mead before bottling? If so, the bubbling could be a sign of an incomplete fermentation. Even Sorbate will can fail to stop an active fermentation.
Age improves with mead, even more than mead improves with age.