Exactly this. I run at 1920x1080 effective resolution on my 15" rMBP, and 1680x945 on my 13". I see the issue on both.
When I switch to the "default" scaling (1440x900 and 1280x800, respectively), it stops. Only the 15" has a discrete GPU, eliminating that as potentially causal.
When I switch to the "default" scaling (1440x900 and 1280x800, respectively), it stops. Only the 15" has a discrete GPU, eliminating that as potentially causal.
The "problem" scaling is 1.5x. The default is 2x.