new tab button does not work

slightly weird but here goes.

ipad2,iOS 5.1.1

the new tab '+' button has stopped working in safari. no response at all, no highlight, nothing.

what's weird is that it's not working in one orientation only, which is the orientation when using the smart over as mini stand, so only slightly inclined.

in the other three orientations it works fine.

the screen location works ok for buttons etc in other apps, e.g google calendar, and locations next to the '+' button in safari work ok.

something that might be related is that I maxed out the number of open tabs befitted it happened, I.e. when opening a new tab, you start to lose tabs of the left hand side of the tab bar.

I've cleared cookie and history data, I've switched off/on a few times but no effect on problem.

looks like a safari bug?

anyone else seen it, any other resolution ?

hopefully tia

yk2