You have created a bootable media with Acronis Backup components and Acronis Universal Restore.
You boot a Citrix XenServer 7 virtual machine with this media.
The media boots directly into Acronis Universal Restore Interface without offering the boot menu where you can choose between Acronis Backup and Acronis Universal Restore.
Citrix XenServer 7 does not support boot menus and thus does not support bootable medias with 2 or more bootable components.
Text boot menu has been added in Acronis Backup 12.5 Update 4 (Build 12730).
As a workaround when using an older build create 2 medias: one bootable media with Acronis Backup components and another one with Acronis Universal Restore.