steamsteam-trading-cards
As I understand it, crafting a set of regular Steam Trading Cards gets you a common Game Badge. I also know that it is impossible to use a mix of regular and foil cards to craft a badge. Either you craft them entirely with Foil Cards, or you use no foil cards. (With the former granting you a Foil Badge instead).
Are Foil Badges instead of or in addition to regular badges? If the former, can you mix and match Foil / Regular levels? What happens?
I know of only one way that this can happen in windows, and has nothing to do with Steam other than their not-so-great decision to install all content into Program Files.
If you are on Windows 7 or Windows Vista, and you have UAC set to ON, then change it later to OFF, this can happen.
UAC does thing evil thing where if a program tries to write to a "protected" area like Program Files, EVEN IF YOU ARE ADMINISTRATOR, when you get a UAC prompt and give permission, it actually writes any files that would normally go into that directory into a "virtualized" directory somewhere else.
If you turn off UAC, that will no longer happen, and as an awesome bonus, it will no longer know about the files that it virtualized.
So in your case, if you had UAC on, installed a ton of games, then later got sick of UAC and turned it off, this would happen as you described.
See the second paragraph in "Features" in the article on User Account Control.
If you have done this and turn on UAC again, your content will come back, but be a TOTAL mess because if you've downloaded more stuff with UAC off, then that will be invisible when you turn UAC on, and vice versa.
this drove me a little crazy once before I realized what was happening.
i'm curious to know if this is your issue.
A few examples:
All Steam seasonal sales so far with ∞ badge levels:
The Steam Winter Sale of 2013 was the first to set the precedent, in which for the first time both foil and regular badges were able to level up as many times possible during the event. This meant that users could easily complete badges and quickly level up their Steam accounts, without a "level cap" on the badge.
A few examples of users with high levels of badges:
From the Steam Winter Sale on out, most of the other Steam seasonal sales feature badges unlimited levels (exception is the Summer Getaway Sale), so theoretically, there's no limit to how many levels you can get with any of those badges.
Best Answer
Foil badges are separate from regular badges, and only have one level. Crafting a foil badge will provide 100 Steam XP, the same as a level of the regular badge.
Source: Steam Trading Card Faq "There is no extra benefit to having foil cards or foil badges aside from their rarity."