Growth theory / Initial GDP: positive coefficient sign
It's really difficult to give a satisfactory answer without having the data at hand. I would do two things:


Check carefully the data and computation of growth rates. By experience, it happens that some "particular" result is the consequence of data or computation issues. You may for example observe any issue by plotting your growth rates and initial GPDs with the name of the countries.
Use your data but exactly the same period, same countries and same methodology than the literature and check if you still find a contradictory result. Then, you can mix: use the same source of data, same countries, same period but your methodology, etc...