Join three tables on same column name

I just tried to upgrade to 0.3.0 and ran into the following issue:

We have 3 tables which all have the call_id column and I want to join them all together:

table output = (
  from hungup
  join side:left beginning [==call_id]
  join side:left accepted [==call_id]
  [...]
)

This now fails at the line join side:left accepted [==call_id] with the error Ambiguous reference. Could be from any of _frame.hungup.call_id, _frame.beginning.call_id.

Is this a bug or do I need to do something differently?