When a piston is placed facing northwards the texture on the top of the piston glitches as shown in the screenshots provided. I am unsure why it does this and have tried in both creative and survival and i find the same results. I understand this isn't a major bug but i still think it should be addressed as i have seen no other complaints about this.
Thank you for your report! However, this issue has already been reported as MCPE-38053. If you have anything you want to say fell free to do so on that ticket. Also, please search for an issue before creating a ticket for it. Have a great day! 🙂