An Odd Problem with IE7/8!

[Manhattan]

Hi there
I'm using rounded corners in my forum, there is a strange problem around them while visit my forum with IE7/8 (you can see the issue in the screen shot below), but the odd point is that sometimes this problem occurs, not always! i.e sometimes it shows perfectly and sometimes not as this image:



How to solve it?
My forum
Any help would be appreciated, guys!
Cheers

[TheJoshMan]

Each time I viewed in IE7/8 the corners were rounded... I even cleared my cache several times and refreshed with the same results...