Tricky scientific (genetic) question

You want to determine the function of a member of an enzyme family capable of phosphorylating other proteins. You do the following experiments:
1) overexpression in fibroblasts – massive substrate phosphorylation – dramatic phenotype
2) knockdown in fibroblasts – substrate phosphorylation unaffected – dramatic, but different phenotype
3) chemical inhibition – substrate phosphorylation unaffected - no phenotype.
These results don’t match. Any idea why?

Thank's for any help!!!!!!!!!