Asked to draft own recommendation letter for faculty application I am applying to faculty positions and two of the people I asked to be my references requested me to draft the recommendation letter.  I am in a STEM field. Is this common practice even when applying for faculty positions?  Should I take it as a really bad sign and try to find other references for the next application I submit?

Writing one draft is daunting enough, but writing two seems even more difficult. I do not know how much the draft will get edited in the end, and I also worry that the two letters might end up looking too similar.  At this point I do wish I had asked someone else, but I do not think I can retract my request.

How can I distinguish the two drafts I write? An obvious thing to take into account is how these two people know me (which will distinguish them). I can also try to introduce differences in tone and style, but doing so feels just wrong.  Yet not doing this risks that it will show through that both were written by the same person.  This is of course assuming that the referees will make only few edits.  Unfortunately I do not know what they will do with the drafts.  If they take the approach form @BrianGPeterson's answer, then there shouldn't be a problem. But I was not asked for a general description of myself or the position. I was asked for a draft.
I request that the students I am to write recommendations for, including recommendations to faculty positions, provide me with an executive summary of the position they are applying for, and a bullet list of the strengths which they would like me to highlight that they feel would be relevant for that position.  

I do not ask them to write the letter for me, just to give me enough input to help write an effective letter.