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#1
Using 10240 build here. I have no problem playing Dota 2 on Source 1 and Reborn which is based on Source 2. Check your GPU driver if it's changed after you update to 10240 because the build upgrade process will always change the drivers to its Windows update version after you do the upgrade.
Can confirm that I have no issues with Source 1 games either. I tried Dota 2, CSGO, and Half Life 2. They all look normal for me. I am using an AMD card with 15.7 drivers.