ERROR: get_child: Index p_index out of size (data.children.size()).

Created by: Listwon

Operating system or device, Godot version, GPU Model and driver (if graphics related): Godot 2.1.x editor, custom build, target=release_debug (no errors in 2.1.4 stable build) Linux Mint 18.2

Issue description: ERROR: connect: Condition ' s->slot_map.has(target) ' is true. returned: ERR_INVALID_PARAMETER At: core/object.cpp:1367. ERROR: get_child: Index p_index out of size (data.children.size()). At: scene/main/node.cpp:821.

Second error repeats "randomly". Every time I move editor window or do something like adding new nodes, it is printed two times.

Steps to reproduce: Just create new empty project.