"Unloading image System.dll" log spam

In the last few releases of Xamarin.Android, we've been seeing an incredible amount of log spam of the following form:

[Mono] Image addref System(0x6ba674c8) - System.dll(0x57b6f3c8): 1799
[Mono] Image addref System(0x6bc55338) - System.dll(0x57b6f3c8): 1800
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x6c159948].
[Mono] Unloading image System.dll [0x6a1d94a0].
[Mono] Image addref System(0x6ba674c8) - System.dll(0x57b6f3c8): 1801
[Mono] Image addref System(0x6bc55338) - System.dll(0x57b6f3c8): 1802
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x6c159948].
[Mono] Image addref System(0x6bc55338) - System.dll(0x57b6f3c8): 1802
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x6c159948].
[Mono] Image addref System(0x6bc55338) - System.dll(0x57b6f3c8): 1803
Thread finished: <Thread Pool> #33
Thread finished: <Thread Pool> #33
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x69789ab8].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1804
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x69789ab8].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1805
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x69789ab8].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1806
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x68e91888].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1807
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x68e91888].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1808
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x68e91888].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1809
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x6b6c96d0].
[Mono] Image addref System(0x69150bc8) - System.dll(0x57b6f3c8): 1810
[Mono] The request to load the assembly System v2.0.5.0 was remapped to v2.0.0.0
[Mono] Unloading image System.dll [0x6a124b10].
[Mono] Image addref System(0x407dc420) - System.dll(0x57b6f3c8): 1811

We only see this in Debug mode. We think it might be related to our networking code. Has anyone else been seeing this? Any idea what's causing it and whether its affecting app performance in general?