When you tap on a date and:
- Get an undesired or confusing Paste option or
- Week Calendar crashes at this moment
this is caused by a large amount of data in your Clipboard.
To empty your Clipboard:
- Start the factory installed Notes app
- Type a character
- Select and copy the character you just typed
- Now go back to Week Calendar, the Paste option should be gone
If this doesn't work just reboot your iOS device.