Why is it annoying to 'draw a bath' but not to to 'draw the curtains'

[TheDevilWearsPrimark]

I have friends who say they are off to 'draw a bath' and it sets my teeth on edge,

MmeCellophane - that would be the letter A my dear

as opposed to an A with an R next to it

we're southern softies so its barth in the Sol household

surely baaa-aaath

Is it because 'a bath' is singular and 'curtains' are plural?

Ahem, actually, I say draw a bath and my mildly humourous DH gets me a pen and paper...does that make me sound stupid? I have always heard it in my family, just thought it was normal.