Many record keepers agree with your boss. As far as I know, the rule is that the 50% balance must be in the account on the day the loan is issued, not for the life of the loan.
I take the conservative position and provide it to all participants and beneficiaries.
However, in late deposit situations my clients usually decide to file the 5330s rather than rile up the participants with the notice.
The assets in the account are not actually security in that sense. The 50% comes in to play only for calculating and issuing the loan. The loan is considered adequately secured when issued, subsequent changes to the account balance does not change that.
From the ERISA Outline Book / Chapter 7