It's not a problem, nothing actually happens. People just build the deflation into the present value.
I don't get how that would actually work. If people are building deflation into the present value now, they will still be doing so in (say) a year, and the two will roughly cancel out.
When you buy a bitcoin, you get two things: the ability to have a bitcoin in a year, and the ability to have a bitcoin any time you would like it in exchange for giving up that bitcoin in a year. Thus a bitcoin today *must* be worth slightly more than the present value of what a bitcoin is expected to be worth in a year because it includes a bitcoin in a year plus an additional option.
That's only true if you can make use of the bitcoin now in a way that's worth more than just having a bitcoin in a year's time, though. It also implies nothing about the value of one bitcoin relative to goods and services now as opposed to in a year's time; the extra value comes from the ability to invest bitcoins in other things.