Using nn.Padding throws luajit: C++ exception

[tastyminerals]

I am using nn.Padding during training and whenever the sequence length is less than 25 we pad the inputs and targets inside nn.SequenceLoader the following way:

function SequenceLoader:sub(start, stop, inputs, targets)
  local seqlen = stop - start + 1

  inputs = inputs or self.data.new()
  targets = targets or inputs.new()

  if self.bidirectional then
    assert(stop <= self.data:size(1))
    inputs:set(self.data:sub(start, stop))
    targets:set(inputs)
  else
    assert(stop < self.data:size(1))
    inputs:set(self.data:sub(start, stop))
    targets:set(self.data:sub(start+1, stop+1))
  end

  -- add padding
  if inputs:size()[1] ~= 25 then
    local pad = nn.Padding(0, 11, 0)
    return pad:forward(inputs), pad:forward(targets)
  end

  return inputs, targets
end

Unfortunately during training this throws numerous assertion errors

...
/home/pavel/torch/extra/cutorch/lib/THC/THCTensorIndex.cu:321: void indexSelectLargeIndex(TensorInfo<T, IndexType>, TensorInfo<T, IndexType>, TensorInfo<long, IndexType>, int, int, IndexType, IndexType, long) [with T = float, IndexType = unsigned int, DstDim = 2, SrcDim = 2, IdxDim = -2]: block: [49,0,0], thread: [125,0,0] Assertion `srcIndex < srcSelectDimSize` failed.
/home/pavel/torch/extra/cutorch/lib/THC/THCTensorIndex.cu:321: void indexSelectLargeIndex(TensorInfo<T, IndexType>, TensorInfo<T, IndexType>, TensorInfo<long, IndexType>, int, int, IndexType, IndexType, long) [with T = float, IndexType = unsigned int, DstDim = 2, SrcDim = 2, IdxDim = -2]: block: [49,0,0], thread: [126,0,0] Assertion `srcIndex < srcSelectDimSize` failed.
/home/pavel/torch/extra/cutorch/lib/THC/THCTensorIndex.cu:321: void indexSelectLargeIndex(TensorInfo<T, IndexType>, TensorInfo<T, IndexType>, TensorInfo<long, IndexType>, int, int, IndexType, IndexType, long) [with T = float, IndexType = unsigned int, DstDim = 2, SrcDim = 2, IdxDim = -2]: block: [49,0,0], thread: [127,0,0] Assertion `srcIndex < srcSelectDimSize` failed.
/home/pavel/torch/install/bin/luajit: C++ exception

What does the error mean?