MiscExp and MiscInc transaction in Moneydance always relate to a specific security, hence the need to select one hence the transaction is recorded as an income or an expense item against that security and either increase or reduce the cash balance in the Investment account. Moneydance uses accounting rules as its basis hence why there is two sides to the transaction, once side here relates to the impact on the cash balance the other is the security that is involved.
It is impossible to make one sided entries in Moneydance due to it using accounting rules.
If you need to adjust a balance in moneydance it is necessary to follow the rules to make it happening. One way of doing this is to create a category, you could call it something like "Investment Adjustments" then use an XFR transaction in the investment account to adjust the balance and using the adjustment category as the transfer source/destination.
If you only need to make a 'one-time' or a 'not-too-often' adjustment to the cash balance, you can do so by entering or editing the 'Initial Balance' value in the account's properties form.
(While viewing the account > MD menu bar > Account > Edit Account)
If I click on "Bank Register" in my same investment account I can easily add a transaction with a category of adjustment without any description. And it seems to put that transaction into the "Register" as I originally wanted. Seems simple, Maybe this is what dwg was talking about except I seem to already have a category called "adjustment" so no need to make a new one.