[Ruby] Failure to properly match correctly balanced code

[metatron-the-chronicler]

Given the following code

module Rfmt
    module Rewriters
        class AlignEq < Parser::Rewriter
            def on_begin(node)
                eq_nodes = []

                node.children.each do |child_node|
                    if assignment?(child_node)
                        eq_nodes << child_node
                    elsif eq_nodes.any?
                        align(eq_nodes)
                        eq_nodes = []
                    end
                end

                align(eq_nodes)

                super
            end

            def align(eq_nodes)
                aligned_column = eq_nodes.
                      map { |node| node.loc.operator.column }.
                      max

                eq_nodes.each do |node|
                    if(column = node.loc.operator.column) < aligned_column
                        insert_before node.loc.operator, ' ' * (aligned_column - column)
                    end
                end
            end
        end
    end
end

I get the following error:

Search failed. This means there is unmatched expression somewhere or we are at the beginning/end of file.

Issue #514 may be related as well.

Note that this code does use tabs.

[Fuco1]

Right, using spaces this parses fine, so I suppose there's some broken regexp somewhere which only uses space and not whitespace.