Hello Przemek,
are you fit enough in php to customize it for yourself?
The following solutions come to mind:
a) downgrade the affected php files to those of version 1.8 (although I wouldn't recommend this approach, it would be the quickest way for you to restore functionality)
b) Adjust the filter order and create an individual filter. The following approach comes to mind (untested):
1. replace the html line breaks with another format of your choice (example: <br /> with #br#)
2. remove all remaining html tags (strip_tags or any other solution)
3. process the remaining output from 4images' own filter
4. replace #br# with <br /> again before the output
This way you keep the line breaks while preserving the previous filter mechanisms.