when using the scalar unit data type the vlue set to the property with thsi value should be 

in the following format: 1024 MB

curently SDC drops the MB sufix

example:

resource-D7c9539373964d74A3b0-template.yml cinder_volume
properties:
size: '(get_input : volume_size) * 1024'
3.2.6 TOSCA scalar-unit type
TOSCA scalar-unit typed values have the following grammar:
<scalar> <unit> , such as 1024 MB

TDP:

https://sdp.web.att.com/fa3ccm1/web/projects/Application_Development_Tools_LM_20.20.01#action=com.ibm.team.workitem.viewWorkItem&id=338620&tab=overview