Hi Sanjay,
I've faced this issue several times.
The only solution we could think of was to value those materials at "V" moving average (so they are excluded from ML revaluation).
Of course this may be difficult if "stock coverage" comes into play.
It just came to me that there might be another option.
I've never tried it so can't be sure that it works.
Please activate actual costing with "2 Activity update relevant to price determination".
With this setting activities are treated in a similar way as materials.
Can you please let us know the results of your testing.
Regards,
Szymon