I'm trying to copy picklist value from related record to another picklist and I tried both, workflow and process builder and I get stuck due to limitations of using a formula for picklists. Here they say they fixed it in Summer '15 but I can't make it work. Any ideas?
I'm sure you've probably figured this out by now since it's been 4 months. Updating Picklist B with Picklist A's value is not possible with a WF field update. Using process builder, you can set Picklist B with Picklist A's value by selecting "formula". Make sure to include the TEXT() function in your formula and it will work!
Check out this screen shot of "real-life" example: