SUMMARY

When opening a previously saved HTML message in the composer to edit it (whether it is a template in the templates folder of the email account, or a regular email that the user wants to "Edit as new"), all the rich formatting related to titles is not properly restored. To be specific:

If some text has the style "Title" applied to it, after saving the message as a template and reopening it in the composer, the text will now have the style "Basic text" and will only be bold (its font size has decreased: the text is as small as Basic Text). The same happens when editing a message as new. 

From a user perspective, the main nuisance is in the template use case since the goal of templates is to have the formatting all set up in advance. Beyond a permanent fix, I would appreciate a temporary workaround if any exists as this is really affecting quality of life for email intensive workflows (customer service, sales, etc...).


STEPS TO REPRODUCE
1. Create a new message with Rich Text, insert some text and give it the "Title" style 
2. Save the message as Template
3. Open the message again in the composer to edit it by double clicking it in the folder template or by using the "Edit as New" option

OBSERVED RESULT

The title has now been switched back to the style "Basic text" and while its boldness is still there, its font size has decreased (it now has the font-size of basic text)

EXPECTED RESULT

The title style should still be present after reopening the message in the composer.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: openSUSE Tumbleweed 20220625
(available in About System)
KDE Plasma Version: 5.25.1
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.2
Kernel version: 5.18.6-1-default (64-bit)