I tested your workflow with 10m_admin_0_countries.shp from data_1_3.zip testdata and, still, cannot reproduce the deadlock.
I tested it on the USA pacific coast area, near the boundary with Canada and I successfully edited the horizontal boundary between the two states (the line belonging to the USA polygon) many times, always cycling through unselect polygon (cycling in the Pacific).
Just one silly doubt: to perform the test I am using the "Edit geometries" Tool. Is it right? You did not specify this but it seems to me the only one suitable for the task.
Marco
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..but before sending it, I reverted to uDig for a "last look" and... ..whoop! It frozed!
In the picture you can(n't) see the Canada polygon on which I just clicked.. ..so something happened AFTER the original polygon was removed and BEFORE the higlighted one was drawn.
So I made this little test: I just started switching selection from Canada to Alaska by clicking first on one polygon than on the ather and back again.. ..keeping an eye on javaw.exe memoy print.
Here the result.
150mb : uDig Just started
168mb: new empty map created
205mb: 10m_admin_0_countries.shp added to map
260mb: click on Canada with "Edit Geometry" Tool
315mb: click on Alaska with "Edit Geometry" Tool
383mb: click back on Canada with "Edit Geometry" Tool
395mb: click back on Alaska with "Edit Geometry" Tool
432mb: click back on Canada with "Edit Geometry" Tool
441mb: click back on Alaska with "Edit Geometry" Tool
504mb: click back on Canada with "Edit Geometry" Tool
510mb: click back on Alaska with "Edit Geometry" Tool
514mb: click back on Canada with "Edit Geometry" Tool
514mb: click back on Alaska with "Edit Geometry" Tool -> uDig frozes!!
So my idea is that "highlighted" polygons objects get in memory an there they get stacked.
This stuff never gets garbage collected.. ..so we might have some serious memory leak problem here!
Also this might be the real cause of the issue: not actually anything to do with editing itself.
