I was at the sea and pondering the Kesef Mishna and the Gra about that argument in Gitin 47. And it occurred to me that that is the whole issue nowadays about shemitaשמיטה the seventh year. In short the question is: Is property that is owned by an idolater in Israel is obligated in truma and tithes or not? The Kesef Mishna [Rav Josef Karo] has two approaches.  One is that as long as that land has not been bought back, obligations like truma and tithe (and thus also shemita) are not applicable. The Gra and the Maharit consider this answer to be a mistake. To them either יש כוח ביד עכו''ם להפקיע מידי תרומה ומעשר או אין לו כוח

Either if the idolater owns the land, the obligations on the land apply or they don't. You can not have it two ways.

This is the source of the  argument between the Gra and Beit Yoseph about the meaning of  יש כוח ביד עכו''ם להפקיע מידי תרומה ומעשר או אין לו כוח Either if the idolater owns the land, the obligations on the land apply or they don't. 

If you hold the idolater owns the land, the obligations on the land do not apply means the land becomes not Israel and needs to be reconquered anew is the Gra and Maharit or it does not is the approach of the the Beit Yosef. Rav Shach I saw has a way of justifying the approach of the Beit Yosef even though it seems to be against the simple approach of the Gemara- But I have not yet had a chance to be able to see what Rav Shach says there.