Russia is in a very strange position in Syria. It’s arguably the key outside actor in the conflict and, more impressively, has decent relationships, or at least working relationships, with most of the other key players, many of whom are in open conflict with each other: the Assad regime, the Saudis and the Gulf states, Iran, Israel, Turkey, the Kurds, the United States. (That last one’s a little more complicated.)
Because of these delicate relationships, Russia does not appear to be in a position to respond or even voice major objections when one of those actors kills its troops, accidentally or in some cases deliberately. This can’t be an encouraging message for the troops and “volunteers” in Syria who Putin is putting in harm’s way.