Since few weeks, an active work have been done with Julien Pontabry and Julien Nardoux to solve this bug report.
On preview screenshots, you can seen a picture resized horizontally to 150%. A preservation mask in green is drawn over the image part to not touch elements during transformation. see below, another example with two area to preserve:
Look like houses are not deformed when image is scaled up horizontally.
This is a companion discussion topic for the original entry at https://www.digikam.org/news/2009-04-25_new_liquid_rescale_tool_under_construction/