[Qgis-user] Shapefile geoprocessing dissolve

[nwastra]

Hi
I am very new to gis.
I have surface hydrology lines in a .gdb file some of which I want to add to the OpenStreetMap.org <http://openstreetmap.org/> . 
In QGIS I select a manageable portion of it, copy features and paste as a new vector layer and save as as shapefile.
The hydro lines are all in many small line segments and I want them joined for each separately named watercourse, so I open the shapefile in QGIS > Select Features by Value, in the box next to ‘Name' I select ‘Is not missing (not null)’, and all the waterways with a name are selected, then I choose Vector > Geoprocessing Tools > Dissolve, choose the selected features of the Input layer, 'Name’ in Unique ID Fields, and save to a shapefile, and Run

This works fine and on opening the saved shapefile in QGIS, I can select any stream and it has a name and the whole stream is selected instead of a small section of the stream as at beginning.

But, when I open it in JOSM (Java OpenStreetMap editor) instead of the entire stream being selected, only a small segment of the lines is selected which is unexpected for me. I wish to use JOSM to merge individual steams into the OSM as it preferred not to have to join all the segments in to one stream each time for individual streams.

Am I missing step/s in the process? - maybe need to merge or join geometry too at the dissolve?

Thanks
Nev

MacOS Mojave 10.14, QGIS 3.2.2 Bonn (kyngchaos)
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