FYI, We just upgraded to version 2.8.1.0. My quote from the above noted post:

"...My validation test involved using two lookup fields, which had cascading filtering applied and with the dependent lookup utilizing a Source View inside the repeating section. That worked fine, so I thought 'problem solved.'

When I turned my attention to an actual form I'm developing for a real business need, the problem wasn't fixed. I suspected it might be the number of controls in the repeating section, so I created a new repeating section and dropping them in (paired with a field label) one by one. It worked okay up through the addition of the eighth control and its label. Upon adding the the ninth, in 'Generate Preview' upon adding a new row in the repeating section, the submit and cancel controls, and the add attachment controls disappeared. My 'real world' form has 13 such controls to be added. Is there a maximum number of controls which can be added to a repeating section? Has this ever been tested?"

Well...it magically is fixed.

Upon saving a version, I noticed one lookup control which I had moved outside of the repeating section had somehow been deleted. I re-created it, then added it into the repeating section as the ninth control and tested. It worked. I added subsequent controls incrementally the repeating section, and they worked, too.

So, something broke, but is now fixed. I don't see that is has anything to do with any kind of maximum number of controls in the repeating section....just some 'ghost in the machine.' So, I'll just note this as resolved flagging this reply as the 'correct answer,' even though no action was really taken to resolve the issue...it corrected itself.