I only just discovered this problem: when Ctrl-Shift-dragging a frame the applied object style scales along with the frame, but when Shift-dragging a frame (applying “fit content to frame” after scaling) the same object style doesn't change size.
After re-examination it seems this only is a problem when, in the preferences, When Scaling is set to “Apply Scaling Percentage” rather than “Apply to Content”. If set to the former I can't seem to undo the style's scaling, in the latter it's a matter of clearing the object override, which is still a pain as I don't want to scale the style in the first place…
Is there a setting I need to change to keep InDesign from scaling my Object Styles? And how do I override scaled Object Styles so I won't have to re-place my images?
Edit: I can't believe I hadn't found this before (I did google before posting) but I found the solution.
If you have this problem, just select the affected objects. Then go to the fly-out menu on the Control panel or the Transform panel and select “Redefine Scaling as 100%”. This will let you clear overrides on the styles that've been applied.