kotlinx.coroutines: rxAwait calls the uncaught exception handler

Why does the following code calls the uncaught exception handler?

As there is an onError supplied I expect it to be called instead.

import io.reactivex.Observable
import io.reactivex.Single
import kotlinx.coroutines.experimental.rx2.await
import kotlinx.coroutines.experimental.rx2.rxSingle
import java.io.IOException
import java.util.concurrent.TimeUnit

fun main(args: Array<String>) {
  Observable
    .interval(1, TimeUnit.MILLISECONDS)
    .switchMapSingle {
      rxSingle {
        timeBomb().await()
      }
    }
    .subscribe({}, {})

  Thread.sleep(1000)
}

private fun timeBomb() = Single.timer(1, TimeUnit.MILLISECONDS)
  .doOnSuccess { throw IOException("") }