When a judgment was rendered regarding the principal, but not regarding the produce - כשעמד בדין על הקרן ולא על הפירות
There is a need for תיקון העולם to explain why we are not גובה ממשעבדי for אכילת פירות; otherwise we may have thought that since there is a קול for the קרן (for which there was a העמדה בדין) there will also be a קול for the פירות.
A creditor collects the improvements - בעל חוב גובה את השבח
A בע"ח collects from the שבח which the יתומים improved (even though they have no recourse), since they are an extension of their father and are required to pay back his loans. However if the improved property was an אפותיקי the מלוה is required to compensate them for their expenses.
You should know; for he writes thus, etc. - תדע שכך כתב כולי
רבא explains; the בע"ח may collect the שבח from the לוקח since the לוקח has recourse. A בע"ח cannot collect פירי from the לוקח and a נגזל can. A בע"ח does not pay the expenses (of the שבח) to the לוקח and a נגזל does.