from Documentation:

Preservation of Symbols on Export

When importing waypoints, the original waypoint symbol is saved internally,
so that the same symbol can be used when exporting - regardless of the waypoint symbol that is shown in ReefMaster.
This feature only works when exporting to the same file format as the original import format.

It this supposed to work with GPX files?

i created a test GPX file from my unit with 7 waypoints with names that match the symbol used
i created a new test workspace in reefmaster
i imported the GPX file.
3 waypoints got reefmaster assigned symbols and 4 of the waypoints got the pin button symbol (ok so far)
i exported the waypoint set as GPX (target hummingbird) overwriting the original file
the waypoint names are correct in the new gpx file,
but the symbols for all the pin button entries went to "Waypoint" instead of retaining their original waypoint symbol