I was downloading a Steam game with terribly slow wifi. I managed to downloaded 6.5 gigabytes out of the 12.5 then shut off my computer because I thought steam would pause it (at previous questions asked about it) But then when I get back on I see it say 125 MEGABYTES. Now it says I have 12-14 hours of download time left and I dont have that kind of time. It doesent matter if it can be fixed, I really just want to know if its a known bug or its being fixed by steam, Thank you.
Closing steam while downloading an application and resuming the download later without losing progress is a feature that is supported by steam. Steam will pause the download when closed and automatically restart it when opened again.
So to answer your question, this is not a known bug and it isn't being fixed by steam currently.
In order for steam to restart the download it needs to have access to the games Local Content. If these files aren't in the file system then it'll have to restart the download. Try navigating to your steam Library folder and see if these files exist. If they do, point steam to them.
If the files don't exist it's possible that your operating system handled them in an unexpected way. This could be the result of countless different variables though. Either way it may be worth submitting a bug request to steam if they aren't there.
Edit: I did some more research on this this morning and found a work around that may of use to you. If your Local Content for the game is available in your file system you should be able to force steam to restart the download where it left off last by copying the downloaded portion from your C:\steam\steamapps\downloading\ folder to your C:\steam\steamapps\common\ folder.