I admit, this whole issue of top, left, bottom, etc., can be confusing! In fact I just had to repeat some photos because I was even beginning to wonder did I give the instructions properly? Here's a suggestion.

Hold your phone vertically, with the home button at the bottom. Now, put a mark of some sort at the top right corner of the screen. This is the camera's physical anchor point for ALL the pictures you take. It does not change. Take a photo. The EXIF info will show orientation as Right top, i.e., the physical anchor point of the camera is in the right top corner of the photo.

Now, hold the camera horizontal, or landscape, with the home button to the right. You will see your mark is now in the top left corner of the screen, i.e. in the upper left corner of your PHOTO when you click the shutter. Now the EXIF data says the camera physical anchor corner is in the Top left corner of the photo. You got this now?

Now, when you post the first picture where the EXIF data says the camera's physical corner is at the Right top corner of the photo, the forum software grabs the anchor point of the photo and puts it in the left top corner of the photo as displayed in the post. To do that it rotates the photo 90° CCW. Now post the second photo. Because the camera anchor point is at the Top left corner of the photo the forum s/w grabs the photo, says, "Ah, the anchor is already at the top left so no rotation is needed."

Open the photo in a photo program and make sure it is oriented the way you want it, and then save it as a new file. What you have done is taken the camera's anchor point that is in the photo EXIF data and thrown it out and replaced it with a new anchor point at the top left. Now the forum s/w will not rotate the photo since the anchor is at the top left corner.

Hope this helps!