Where are you changing the units? Don't use the Units command. Set them in Ambient Setting. Go to the settings tab in the Toolspace. Rt click on the drawing and select Drawing Settings. Check both the Units tab and the Ambient Settings tab.
Then you posted to the wrong forum... This one is for Civil 3D. You want the Land Desktop forum.
I never had Units change by themselves on me in Land Desktop, but it's been so long since I've used Land Desktop that I probably can't provide any insight. The only thing I can think of is to make sure you don't have any Lisp routine or anthing like that which might be changing them on you. Someone in the Land Desktop forum may be able to help you sort it out.
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