It was discovered that one of the mods uploaded used content found in another mod and they used it without its creator’s permission. However according to the modder, they claim that Valve had told that if the content used was free and separate to begin with, it was alright to be included in their mod and sold for a price.
The creator of the mod whose content was used was not too pleased about this, unsurprisingly, but it looks like the mod has since been taken down in good faith and both parties are apparently in talks to work it out. Like we said this is a rather tricky situation and one that Valve might not have considered fully.
In some ways it is similar to how real-life newspapers or magazines source or quote articles online without the proper credit or permission and sell them for a profit. Of course Valve’s new mod program is still new and there are bound to be teething issues, so hopefully things will start running more smoothly in the weeks and months to come.