JavaScript about types causes editor to stop working

I got this error while working on building a simple program:

```
Uncaught Types do not match, when trying to type Number
Type.apply @ blockly_compressed.js:1205
(anonymous function) @ blockly_compressed.js:1239
Blockly.TypeInf.inferWorkspace @ blockly_compressed.js:1238
Blockly.Connection.connect_ @ blockly_compressed.js:926
Blockly.RenderedConnection.connect_ @ blockly_compressed.js:1322
Blockly.Connection.connect @ blockly_compressed.js:932
Blockly.BlockSvg.onMouseUp_ @ blockly_compressed.js:1345
e @ blockly_compressed.js:1693
```

After this, many parts of the editor stopped working. It's as if none of the event handlers work at all any more.