epub to azw conversion is adding line heights ?

[stumped]

epub to azw3 is adding line height declarations to CSS - is this a bug & can this be disabled ?
I do not recall seeing this in the past, so maybe it did not happen in older versions of calibre. My sideloaded azw books look awful after such conversion - lines are far too close together, and the device options do not expand them.
( I tried disable font scaling in conversion preferences - that had no effect )

I removed all line heights from each class of the epub css before converting it e.g.
.calibre {
adobe-hyphenate: none;
display: block;
font-size: 1.1em;

margin-bottom: 0;
margin-left: 5pt;
margin-right: 5pt;
margin-top: 0;
orphans: 1;
padding-left: 0;
padding-right: 0;
text-align: justify;
widows: 1
}
but in every class in the AZW css, there is now an added line-height delcaration ( I have marked it in bold below) e.g.

.calibre {
adobe-hyphenate: none;
display: block;
font-size: 1.1em;
line-height: 1.2;
margin-bottom: 0;
margin-left: 5pt;
margin-right: 5pt;
margin-top: 0;
orphans: 1;

PS a conversion from epub to mobi looks equally bad.

it is not an issue with the specific book, I converted another chosen at random eub with same outcome.

PPS I stumbled across another bug ? or install error? I went to preferences to inspect all the conversion options, but when I click on output options I get
ImportError: No module named output_config
- here is the detail:
calibre 2.56 [64bit] embedded-python: True is64bit: True
Windows-8-6.2.9200 Windows ('64bit', 'WindowsPE')
('Windows', '8', '6.2.9200')
Python 2.7.9
Windows: ('8', '6.2.9200', '', 'Multiprocessor Free')
Successfully initialized third party plugins: DeDRM && K4PC, K4Mac, Kindle Mobi and Topaz DeDRM && Inept PDF DeDRM && Inept Epub DeDRM && Count Pages && Copy Cover To Device && Quality Check && Modify ePub && Open With && Overdrive Link && Resize Cover && View Manager && Open EPUB In Editor && Overdrive Link
Traceback (most recent call last):
File "site-packages\calibre\gui2\preferences\main.py", line 292, in show_plugin
File "site-packages\calibre\customize\__init__.py", line 663, in create_widget
File "importlib\__init__.py", line 37, in import_module
ImportError: No module named output_config

[jackie_w]

In your conversion settings have look at Look&Feel - Fonts tab: Minimum line height. It may be set to the default of 1.2%. I have mine disabled, i.e. set to 0.0%. This is the explanatory ToolTip:

The minimum line height, as a percentage of the element's calculated font size. calibre will ensure that every element has a line height of at least this setting, irrespective of what the input document specifies. Set to zero to disable. Default is 120%. Use this setting in preference to the direct line height specification, unless you know what you are doing. For example, you can achieve "double spaced" text by setting this to 240.

[stumped]

that was it, thanks