Mac Acrobat signature does not stay in field

For Mac 10.11.6 and Acrobat 11.0.17, Initials can be dragged to the field and then remain, but signatures when they are dragged to the blue field, disappear and the field goes white with no signature visible. You can copy and paste a signature image into the field, but cannot use the Place Signature tool within Fill & Sign Tools window.

Is this a known issue or can it be fixed ?