gimp-drawable-transform-perspective doesn't work when asked to enlarge a layer

Question

I'm using Python to develop a GIMP plug-in. I make use of the gimp-drawable-transform-perspective function called this way:

pdb.gimp_drawable_transform_perspective(
                layer,
                rect.x,  rect.y,
                rect.x + rect.width, rect.y,
                rect.x,  rect.y + rect.height,
                rect.x + rect.width, rect.y + rect.height,
                TRANSFORM_FORWARD, INTERPOLATION_CUBIC, True,
                3, TRANSFORM_RESIZE_ADJUST)

Where rect is a custom structure representing a rectangle. The problem is that when I try to enlarge my layer using this method, the transformation seems to crash (even though no errors are reported) and the result is that I get only part of the initial layer on the image. Like if the function had done half the job and decided to stop.

I'm using the GIMP version 2.6.11-2ubuntu4.