To me this sounds like pretty standard MicroB behaviour. It has behaved like this since the first firmware versions, or atleast on my device.

MicroB often receives criticizm for "tearing", which looks just like what the OP is describing. I believe it had something to do with the browser's memory handling. It "forgets" parts of the page and sometimes a good ol' CTRL + R is the only thing to set things straight again. Since it seems to be so closely linked to changing between tasks, a memory-related reason is suspect #1 for me.