Empty text items aren't found by "find enclosed". Tcl/Tk 8.4.19 and 8.5.2 don't have the bug.
Script:
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catch {console show}
canvas .c
grid .c
puts [info patchlevel]
set item [.c create text 100 100 -text "1"]
puts "Enclosed: [.c find enclosed 0 0 10000 10000]"
.c itemconfigure $item -text ""
puts "Enclosed: [.c find enclosed 0 0 10000 10000]"
-----
Result:
8.6.0
Enclosed: 1
Enclosed:
confirmed
Bug first appears in checkin
http://core.tcl.tk/tk/ci/6c007ba101
which was intended to fix 2328657