Mini Cart random problems

[enock]

J2.5.2 VM2.0.3B
Development site http://www.loti.com.au (yes it is slow but it's on a VPS which process hit 5 whenever VM is loading)

I'm getting a random issue with the popup cart - if I click add to cart I get the following popup and result (even clicking on the same button)

Popup shows continue Shopping BUT not Show Cart - product not added to cart
Popup shows continue Shopping BUT not Show Cart - product IS added to cart
Popup shows continue Shopping and  Show Cart - product IS added to cart (if the popup displays Add to Cart then the product is always added to the cart)

Being random I can't find any settings etc at issue