The effect is somewhat inconsistent, but in general can be seen when text with a character border or area color formatting extends across multiple lines, whether by automatic line breaking, manual line breaks, and even paragraph breaks.
I believe you can get the effect even when short segments of text cut across lines, but it is easiest to demonstrate with very long segments.
I've provided an example with character borders.
Testing now with v220.127.116.11, but it's been around for several major versions.
Steps to Reproduce:
1. In paragraph formatting, set line spacing to "fixed" and choose a size noticeably larger than the font size
2. In character formatting, set character border or area.
3. Input text with this formatting that extends over multiple lines, via automatic line breaking, manual line breaks, or paragraph breaks
Height of the border or colored area is inconsistent from line to line.
Height of the border or colored area should be the same as the character height (?), or perhaps the full line height, but not randomly switch between the two.
User Profile Reset: No
It's not clear to me what the correct behavior should be. It's not possible to configure line height and interline-spacing independently in LibreOffice, since each "line spacing" option works differently.
Created attachment 159203 [details]
Test document demonstrating issue
Created attachment 159204 [details]
Exported PDF of test document
Build ID: 169a10f0e4680814145b668c6320be04038d7a89
CPU threads: 4; OS: Linux 4.19; UI render: default; VCL: gtk3;
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Build ID: 5b168b3fa568e48e795234dc5fa454bf24c9805e
CPU Threads: 4; OS Version: Linux 4.8; UI Render: default;
Locale: ca-ES (ca_ES.UTF-8)
in previous versions, the border are not even imported
Behavior of character border is not yet specified. It is still not clear, what should be the "correct" behavior. CSS, means browsers, and Microsoft Office do it different.