LTC490 wiring caused short
It's really good you solved the main part of this yourself - not an uncommon problem getting Vcc and ground wires mixed up.


  Slightly unrelated, but the test schematic includes capacitors and a
  resistor (Figure. 2 in the datasheet). Can anybody tell me what these
  are needed for?


Figure 2 is not a recommended circuit for anything other than testing the chip's timing diagram. If you read the "Switching characteristic" section on page 3 it adds those capacitors to presumably simulate the effect of cable capacitance. 100 pF is usually about 1 or 2 metres of cable.

Figure 5 is a typical setup and you should consider using 120 ohm resistors to match the cable impedances but, if cables are short and datat rates are low you can usually get away without: -