errors[:base] is cleared when entering model

Hello,

when using

@booking.errors.add(:base, "Only " + reservable_machines_count.to_s + " " + MachineType.find(type).name + "(s) available at the choosen date.")

or

@booking.errors[:base] << "Trying to book more " + typename + "s than existing."

in the controller, results in an empty array in the validation methods of
the booking model. I do not call errors.clear.

Example code:

controller:
# returns string from above (correctly) puts "Errors before calling model" + @booking.errors[:base].to_s ... respond_to do |format|

  if @booking.save
     format.html { redirect_to(@booking, :notice => 'Booking successfully created.') }
     format.xml  { render :xml => @booking, :status => :created, :location => @booking }
  else
     # this line only contains the errors setup within the model, original ones are gone. (WRONG)
     puts "Errors after model" + @booking.errors[:base].to_s

model:

validate :has_one_or_more_reservations

def has_one_or_more_reservations

  # this one is empty as well
  puts "printing errors : " + errors[:base].to_s
  errors[:base] << "No machine selected" if (reservations.nil? or reservations.empty?)

end

Actual codebase can be found on http://git.schottelius.org/?p=mbs;a=summary.

Tested with rails 3.0.0 and 3.0.3.