Image roipoly and DataCursorMode problems with AlphaData property

I've developed an image analysis tool for viewing/analyzing/processing medical images (MRI, CT, etc.) which has an overlay option which uses the image's AlphaData property as a mask. However, when I try to use the roipoly function or the DataCursorMode the images disappear after the first buttonpress. This only happens for me when AlphaData is non-scalar, and also only within my custom class. Also, to reset the image all I have to do is click the Show Colorbar option on and off. I'm currently running Matlab on a UNIX system.

Does anyone have any idea what might be going wrong?