Yes, the reason the prior year is re-opened is so you still have your current year to prior year comparisons. If you re-close the prior year, you will then lose the comparison report for that year. Here is an explanation of what occurs when you convert to version 7.0.x or higher of MultiLedger:

Version 7.0.x & higher has doubled the number of months you can have open from versions 6.0.x and earlier. You can now work with 30 months (2 1/2 years) open. When you convert your current files to MultiLedger 7.0.x or higher, you will have the prior year, the current year, and six months into the next year available to enter transactions. You can enter new transactions, but you cannot modify any transactions from the prior year. Since that year had been closed, the transactions are no longer available, but the balances and outstanding receivables and payables carry forward.