I am trying to reduce the height of a swimlane in Microsoft Visio 2013 using drag and drop as usual but it doesn't seem to work:

I then tried to change the height property in the ShapSheet:

but 31.7333 mm seems to be the minimum.
Is there any other way to reduce the height of a swimlane? Its minimum height seems to be locked somewhere. I did look in the swimlane's container ShapSheet: nothing caught my attention but some properties are pretty esoteric to me.
Following Devid's answer, I unchecked the height protection for both the swimlane and its container, although it does sound like the solution it didn't help:
Swimlane's protection properties:

Container's protection properties:

Protection properties of the container of the container:

I use Microsoft Visio 2013 Professional on Windows 7 SP1 x64 Ultimate.
