FileMaker Server 188.8.131.52, 6GB of Ram Cache (also tested with 512 MB)
Server: Mac OS X 10.10, Mac mini, i7 2 GHz, 16 GB of RAM.
One WebDirect user while testing. No other services than FileMaker Server Active.
Wifi access to relatively fast network.
WebDirect, very simple layout, only one table, no relations, no script triggers.
While entering text into a standard text field every 3-5 seconds the entire screen redraw/flicker without any obvious reason.
Please see the enclosed QuickTime movie.