Or did they? My understanding is that the Germans on the eastern front relied heavily on mines to supplement their lack of defensive numbers, especially in the lead up to Bagration in Belorussia.
At the same time, we never really hear about the kinds humanitarian tragedies that resulted after the fact in other mine ridden areas. How come? Did the Soviets just not make that public or were they removed?
I don't know much about problems that leftover minefields have Cambogians, Iranians or another places that suffer from war, so I can't say how much problems have Soviets in comparison.
But USSR suffer from this problems after war. It sometimes called as "echo of war" ("Эхо войны") and was constant problem from the end of war to our days - even just in start of this September in Peterburg founded few shells.
USSR start operations for seeking and deactivating minifields as early as they start control area - for example in Novgorod oblast officialy start in 19 Febrary 1944 г, after liberation most of oblast and officialy end in end 46, when most of minefields and shells was removed. But some leftovers still be problem and after 47 it mostly tested by local military regiments next few decades.
I don't really sure what you mean when say "we never really hear about the kinds humanitarian tragedies" - because I never hear about scale of "humanitarian tragedies" in Cambogia or in Iran. But this problem never was secret in USSR - actually trope "Somebody find old mine/grenade/shell and something did with it" is very common both in post-war literature, "folcklore" like jokes or personal stories (I hear at least from three different people how they find shells, grenades or rounds. Two of three is contined with "we make bonfire around them to look how they explode") and in movies too.