Strange. Which OS and version do you use? Which screen version do you use?
I'm on Ubuntu 14.04 with screen version 4.01.00devel (GNU) 2-May-06 , and I don't have any issues with it (though I have with tmux :) ). See this thread for screenrc and for further details.
https://groups.google.com/forum/#!topic/pyroscope-users/_5yMqjIHcpoI'm using Putty 0.64 beta on Win (no issues again), under :
- termnal: x "Use background colour to erase screen"
- colors: set "Indicate bold text by setting: both"
- appearance: x "allow selection of variable pitch font", Font: DejaVu Sans Condensed, size: nine
This DejaVu font was the only one (that I tried) which can display all fonts and text is still readable. Not perfect, but close :)