Crash when creating custom label

[peterva]

Hi, I am using the MultiVariant custom field plugin for managing colours and sizes in my webshop. After upgrading to VM 3.0.12, I get a 500 server error when adding a custom label.

Step to reproduce:
edit a product
enable the multivariant plugin on the custom fields tab and 'save'
choose 'custom label' in the dropdown and click 'new'
fill out the custom labels in the text area
click save --> crash (Failed to load resource: the server responded with a status of 500 (Internal Server Error))

I am using VM 3.0.12 on Joomla 3.4.5. Help = much appreciated, the plugin worked fine on VM 3.0.10.