Weird Rendering Issue

Hi All,

gotten a weird rendering issue, when editing large files, it seems the whole vim goes cranky (Look at the status bar, it become 2 lines when in actual fact, it should be only 1). image attached. this is considered trival, sometimes, it seems the whole file got corrupted and becomes very messy. i have to reopen vim but the next time i write to a file again, it comes back.