Likely not Linux-specific.
Is it worth contacting steam support about this issue? I was really looking forward to do a Professor's Speks exchange with my friend.
It can't hurt.
It seems the effect was only temporary, and it has worn off by now.
I passed this on to the TF2 team and they indicated there was some caching in the system that could hold things over for a period, which lines up with the effect going away after a while. They don't think there's an actual exploit here.
Nothing extracted yet.
Steps to reproduce:
The downside is that the "who helped you the most" popup for giving away the Professor's Speks will not appear. I haven't tried whether a normal way of upgrading (buying orange box, buying something from mann.co) adds this notification or not, but I suspect that it doesn't.