LG
I trade both in IRAs and Margin Accounts. Many brokers either misinterpret the rules, or ignore them. It is my understanding that one may trade in an IRA up to the total amount of "cleared" cash available in the account at the beginning of that trading day. One can do 50 roundtrips if one so desires as long as one does not exceed one's cleared cash -- in other words no same-day reuse of proceeds from that days' trades, but PDT rules do not apply.
On the other hand, in Margin Accounts one can reuse cash all day long, but must maintain a $25K minimum balance in the account to avoid PDT status. A margin account with less than a $25K balance will allow only 3 roundtrips in 5 trading days, and you will be block from placing the fourth trade within that timeframe (you can still sell or buy-to-cover anything already held in the account, just cannot open a new position). You can remove this constraint by depositing funds to bring the account over $25K again.
That said, of my 5 or 6 online brokerage accounts, TradeStation is the only one whose lawyers advise them to apply PDT rules to IRAs, which I think makes no sense since, unlike a Margin Account, you cannot simply put additional funds into an IRA to achieve the $25K minimum for exemption from PDT rules applied in Margin accounts. I had quite a go-round with them about it a year ago, and ended up not opening my IRA there.
Hope this helps.
N2B