createchangelog version logic does not work properly

Preconditions:

qt5.git cloned, 5.12.10 branch in use with latest content.

Create change files for  5.12.10 release using latest 'createchangelog' go script. 

Expected output:

Change file with correct version strings in the change file header. Expected versions are  current version 5.12.10, last version 5.12.9 and last minor version 5.11.

Actual output:

Change files are not created. 

 
"Detected current version 5.12.10 is not newer than last tagged version 5.15.1 - no changelog to create"
 
After hard-coding '5.12.9' as the last version the change files area created with header:
 
"The Qt version 5.12 series is binary compatible with the 5.14.x series.Applications compiled for 5.14 will continue to run with 5.12."
 
Hard-coding last minor to 5.11 sets the change file header right.