[Collector]

As of the 'GR2' evasion update, I have been unable to place furniture within my house at all. Already placed furniture can still be moved. 

This issue has persisted through multiple restarts.

Other building features appear to be unaffected.

[WaifuApple]

This issue is a BYOND version issue, and the recommended solution currently is downgrading to BYOND Version 513.1542.

You can find it here: http://www.byond.com/download/build/

[Neus]

As Appo said, this is an issue with your BYOND version.