Fixed (in branch text-elided) bad counting of the total number of vertical pixels in the text widget, resulting in small change of the Y scrollbar size. Happened because CalculateDisplayLineHeight expects an index at start of a display line, which was not always the case.

Test case 'J':
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package require Tk
entry .e2 -justify center -width 50
pack .e2
pack [text .t -width 30 -yscroll ".s set"] [scrollbar .s -command ".t yview"] -side left -fill y
pack configure .t -expand 1 -fill both
for {set i 1} {$i < 25} {incr i} {
    .t insert end "Line $i\n"
}
wm geometry . 300x200+0+0
.t tag add hidden 5.7 11.0
.t tag configure hidden -elide true
update
set y1 [lindex [.t yview] 1]
.t count -displaylines 5.0 11.0   ; # makes scrollbar change size!
set y2 [lindex [.t yview] 1]
.t count -displaylines 5.0 12.0   ; # makes scrollbar size OK again!
set y3 [lindex [.t yview] 1]
list [expr {$y1 == $y2}] [expr {$y1 == $y3}]  ; # shall be {1 1}