I just tried the "^" character, and the "~" character. Both are resulting in the same truncation.
In addition to the TAB completion, I also see this when using the FCalc plugin:
I can type ~fc 3+3, and it will show me the answers. Normally I can just press enter, and it will blank out the 3+3 and let me do another claculation. Now, however, when I press enter, it reverts to just fc, which, without the prefix, doesn't trigger the plugin.