using --lossy_transparent option sometimes results in higher file size

[Faalagorn]

It seems that using --lossy_transparent option sometimes results in bigger files, my wild guess is that it may be related to alpha transparency, but I may as well be wrong here's one of the files that behaves as such (original file saved by GIMP attached):

[faalagorn@faalagorn-pc unopt]$ zopflipng location_restaurant_generic_01_8+9+10+11.png location_restaurant_generic_01_8+9+10+11.png
Optimizing location_restaurant_generic_01_8+9+10+11.png
Input size: 22065 (21K)
Result size: 17562 (17K). Percentage of original: 79.592%
Result is smaller
File location_restaurant_generic_01_8+9+10+11.png exists, overwrite? (y/N) y

[faalagorn@faalagorn-pc unopt]$ zopflipng --lossy_transparent location_restaurant_generic_01_8+9+10+11.png location_restaurant_generic_01_8+9+10+11.png
Optimizing location_restaurant_generic_01_8+9+10+11.png
Input size: 17562 (17K)
Result size: 17933 (17K). Percentage of original: 102.113%
Preserving original PNG since it was smaller