That's very interesting mine sound pretty similar but are never normally timid they are normally right there watching every movement I make. When you say 'startle' them it actually made me think maybe I did scare him a bit considering it was night time and most lights apart from their tank light were off, he may not have seen me clearly and got spooked but its just strange because I've never had an issue in the last 3 months of owning them. I got them as a pair when they were quite young and they have now matured and are getting ready to breed (I think, and hope). It's good to see its not just me as it actually was quite sad to watch I couldn't understand the issue as all the other fish were fine so I knew it wasn't water parameters.
Thanks for the reply Schwack