You're having trouble saving a Dimension Style (DimStyle) to make it the default for either site or detail dimensions.
You might go into the General Preferences, click the Save DimStyle button, and receive confirmation that you have set the style you want as current. However, when you go to place a dimension in Model Sspace, you might find that our software uses a default DimStyle (not the one you saved in the Preferences).
Once a DimStyle is defined in a drawing (that is, once you've placed a dimension that's assigned a particular DimStyle), our software will continue to use that one. The DimStyle saved within Preferences is merely the revised default.
Whether we're talking about your library of existing drawings, or just the drawing you're using to test, you can resolve this issue by either renaming the current DimStyle or deleting the Land F/X DimStyles from the drawing.
Doing so will force the system to re-create your DimStyle from the revised defaults.