Two things that I'd suggest:
First, try it without Optifine installed and see if you get the same result. It might be a bug with Optifine.
Second, your texture isn't a power-of-two resolution. Try changing it to either 512x256, or up-scaling it to 1024x512. Minecraft strongly prefers square numbers.
I hope that helps you.
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Tried it again on vanilla with a resolution of 960x480.
And then again with optifine and a resolution of 512x256
Apparently it's just a bug with Optifine.
Thanks.
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[Redacted by user.]
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The most irritating thing that happened to me in Minecraft is this: I was playing in survival, mining, and I found some diamonds, (About 5 diamonds) I took them back to my house. I had to log off for the day. The next day, I log back on, (I'm on a survival server) and ALL of my stuff is gone, including the diamonds, the only thing left is a giant crater where my house was. I told the admin about it, and they ignored me and banned me for hacking because of the giant crater. I don't remember what server it was, but the admin were evil towards me.