Minecraft Username:
subxplorer

Brief Description:
When holding a Diamond left click a Trade Sign, an error message will be displayed.

Instructions:
1. Hold a Diamond in your hand
2. Left click a trade sign

How many times did you recreate this bug?:
20 + times at different locations

Result:
When a Trade Sign is left clicked while holding a diamond an error message is displayed that says, "You are not permitted to do that, Are you in the right mode?"

Expected Result:
No message should be displayed.

Evidence:
Too lazy to post a screen shot, but it is easy to duplicate.