When using the_post_thumbnail() and setting the size via an array, if either dimension matches a preset size then the preset is used instead of the requested size.
There is no note about this in the Codex documentation (http://codex.wordpress.org/Function_Reference/the_post_thumbnail)
It also appears in the wild without clear resolution...
the_post_thumbnail( array(123, 150) ); // get thumbnail of 150x150 -- NOT 123x150 as expected
Set your requested size to something similar, but not exact (i.e. 123x149 or 123x151).
Is there a bug report somewhere that I can follow that reports on the status of this issue?
Can the Codex be updated to note this caveat?
(I'm trying to follow the Bug Submission guidelines - http://codex.wordpress.org/Reporting_Bugs)