IBooks display inverting colour unexpectedly

HI,

since I upgraded to ios8 iBooks has intermittently switch fro normal w on b, to b on w. Sometimes it switches back, sometimes I have to close and reopen the ap. Occasionally some text highlights itself . I've checke Accessability and its on the normal w on b. The screen flickers once I a while. I,m up to iOS 8.3 and none of the upgrades have fixed it. It's very irritating. Any suggestions?