Different behavior of OOTB Blog list while versioning

Per my understanding Post list behaves differently from other SharePoint list types when it comes to content approval and versioning. Please check the  following list(see the underlined lines). I doubt this is a bug with the product...

Post List:

if Content Approval Reqd=No AND  Versioning = No     : No version created on saving existing blog posts, Save As Draft option not available

if Content Approval Reqd=No AND  Versioning = Yes    : Versions created on saving existing blog posts, Save As Draft option not available

if Content Approval Reqd=Yes AND  Versioning = No    : No versions created on saving existing blog posts, Save As Draft option available

if Content Approval Reqd=Yes AND  Versioning = Yes  : No versions created on saving existing blog posts, Save As Draft option available

All other list types:

if Content Approval Reqd=No AND  Versioning = No     : No version created on saving existing blog posts, Approval option not available

if Content Approval Reqd=No AND  Versioning = Yes    : Versions created on saving existing blog posts, Approval option not available

if Content Approval Reqd=Yes AND  Versioning = No    : No versions created on saving existing blog posts, Approval option available

if Content Approval Reqd=Yes AND  Versioning = Yes  : versions created on saving existing blog posts, Approval option available