I've been aware of the validate steam cache files for a while.You can do it manually from the properties tab by right clicking in the game list.It messes up everything; make you wait or worse, redownload and downgrade the version/files of games which uses launchers.So, how to disable/prevent Steam to automatically and randomly validate game caches/files?Interesting, I've definitely seen this redownload an exe when I've manually patched the exe so it's checksum would be different.I wonder if the fact that it was completely missing prevented it from redownloading. It compares the game files you have on installed your computer with those of of the latest version on the steam servers.I recently posted this to the Steam Community, thinking that was a more appropriate place for it..they were useless (see for yourself), and I've always gotten better answers from Tom's users, so I'm hoping someone might have some insight into this.
As to why the validation is happening automatically after updates download for these two games.
If something goes whacky with your game, this sometimes fixes it.
Steam support suggested it once and it got me out of a problem I had, so I try it again on occasion.
My Steam wants to validate TF2 at least every other day for some reason, which takes a good 5 to 10 minutes.
Both were free and both download updates incessantly, so I uninstalled them.