Venture Capital investments are still investments, and transactions need to be posted as any other investment transaction.A capital contribution is considered a "buy" and a distribution is considered a "sell" or "return of capital". (You can sell 0 shares and the system will show it as a return of capital.) If you want your cost basis to be affected, this is how the transactions need to be entered. (This requires an investment format type.)
See last entry on the Forum Post Investment Entries for a list of investment format types.
If you want to set the investment up as an Investment Receivable format type (or any non-investment type format), then you will have to manually change your cost basis balance with each transaction but you won't have to "buy" or "sell". Your balances will always be correct, but your cost basis will not be affected by your transaction entries.