In the 'display and monitor' section I changed my screen orientation to 90 degrees clockwise. After clicking apply my screen rotated 90 degrees. I changed orientation back to normal, but when I click apply it just sets orientation back to 90 degrees and doesn't rotate my screen. I can switch between 90 degrees clockwise and counterclockwise, but won't change to either normal or upside down. I had to switch from HDMI to Displayport to fix the problem. I tried again with DP and the same thing happened. I had to switch to DVI to fix it and I'm not about to try again because I don't have another port to switch to. I am very upset about this. To say this is a serious problem is an understatement. Reproducible: Always
Wow, almost a whole month and not a single reply. I guess you're all busy with the massive amount of other bugs plaguing Plasma atm... Anyway, I figured out I can fix this by changing the screen orientation in Nvidia X Server Setings. I'd guess this is only a problem for Nvidia users, but not a problem with the driver since the setting can be changed in System Settings but not reverted.
Sorry for the long turnaround time. Could you check if this works with Plasma 5.8? We've had a problem updating the screen size in this scenario, which leads to your bug.
Yes, it seems to be fixed in 5.8.