Problem with wrong calculated boundary box

I think that I might have a problem with osmosis tool, while importing osm.pbf file into graphhopper a boundary box on the map is placed with coordinates: "bbox": [0.090027, 0.246737, 0.10008, 0.255576]

But from beggining. What I want to achieve is to merge my local edited map with official OSM map, and upload result to my local OSM editor. In shortcut main pipeline goes like:
1) Download osm.pbf file from geofabrik.de
2) osmosis --read-pbf file=$ORIGIN_PBF_NAME --sort --read-pbf file=$EDITED_PBF_NAME --sort --merge conflictResolutionMethod=lastSource --write-pbf file=$FINAL_PBF_NAME
3) osmosis --read-pbf file=$FINAL_PBF_NAME --write-apidb host=$DBHOST database=$DBNAME user=$DBUSER password=$DBPASSWORD validateSchemaVersion="no"

The $FINAL_PBF_NAME file which is merge result I can load into graphhopper, but I cannot use it because boundary box is between coordinates which I posted in earlier.

What is curious? When I simply download plain new osm map from geofabrik, than upload it to DB and back save to PBF file with scripts:
1) osmosis -v --read-pbf file=$FINAL_PBF_NAME --write-apidb host=$DBHOST database=$DBNAME user=$DBUSER password=$DBPASSWORD lockTables=no validateSchemaVersion="no"
2) osmosis --read-apidb host=$DBHOST database=$DBNAME user=$DBUSER password=$DBPASSWORD validateSchemaVersion=no --log-progress --sort --write-pbf file=$LATEST_PBF_NAME granularity=10000

than boundary box is calculated correctly around my map area.
I've read osmosis documentation in this topic, but I didn't find anything related to.
Can anyone tell me what exactly is bbox and how it's generated? Can I somehow override or set those values while saving to osm.pbf file?
In additional what is unclear for me- is those values stored somewhere in postgres DB or it's calculating "on the fly" by external tools (i.e. graphhopper) based on some osm properties?

What I suspect is that during merge I might loose some informations.

Any suggestions are apprieciated.