The limits on the layer manager and position tabs are different and can cause controls to become disabled. Reset All on the Positon tab doesn't reset everything.

Example using 1920x1080
Set a layers X position to -2000 on the layer manager
Go to the Position tab and Pan X slider is disabled as it is less than -2
Set Zoom to 5
Go back to the Layer manager and the width is listed as 8192 rather than 9600 (5x1920), the height is correct at 5400 (5*1080)
If you then try to alter the height X goes more negative, until it his -10000, whether you try to increase or decrease the height.
Go back to the Position tab, click Reset All to get out the mess and some sliders remain disabled and Pan X is -7.15 for me.
Go back to the Layer manager and X shows as -6864. Clicking reset there then gets everything reset.