If you updated Magento to the latest version 1.9.3 you noticed that there are many changes done to Magento core and that some of the extensions doesn’t work properly anymore. So be sure to check patch noticed to avoid issues and it is highly recommended to make upgrade on development server first.
One of the issues that you may encounter is that MAGMI does not import multi-select attributes anymore. We found that Magento has changed attribute type for multi-select attributes from VARCHAR to TEXT, probably due limitations that existed with number of available attribute options in VARCHAR configuration (limitation for number of characters per field).
MAGMI still looks for multi-select attributes into VARCHAR attribute type and since it’s not there he can’t assign proper ID to that values. It is possible to replace attribute option labels with attribute option IDs and in that case it might work, however we didn’t had enough time to test this option properly (also modifying CSV file can be very time consuming).
So we decided to created patch for MAGMI that will correct this issue, until official update is available. We are not responsible for any unwanted actions that might be caused by this patch and so far we didn’t encounter a single issue, after extensive use on several big projects.
Patch is created by my colleague Dr. Srdjan Janjic, Magento developer at SMDesign Studio