Incorrect green and red figures unless I log out and back in - any one else have this?

This is quite scary - I look at my position, put a trade on then the next time I look it is different as if my trade was matched even though it never seemed likely to have spiked to that price and back while my back was turned. But had I believed the figures  I might have put on an opposite trade and the found myself in deeper water than I thought. The only way I could tell something was up was because the seemingly more balanced position should have released a lot more of my funds into my account balance figure.

The solution seems to be to log out and back in, or clearing the BF cookies (which means logging n again anyway).

Has anyone else had this? Is it a BF or (Chrome) browser issue or just somethung to do with my laptop needing more memory?