But why would Hungarian stamps be overprinted with the Romanian royal crest?
In short, Hungary was invaded by Romania in 1918 and Romania overprinted Hungarian stamps found. This is either the oval overprint ("First Debrecen", named for the captured city), or the round overprint ("Second Transylvania"). Both exist on other Hungarian issues of the time.
There are many, many forgeries around. Another reference:http://postww1stampforgeries.org/hu...n-1st-issue/http://bigblue1840-1940.blogspot.co...fficial.html
The 5f harvesters has a genuine First Debrecen overprint, the postage due does not (sorry, Big Blue).