sed in while read loop doesn't complete commands

I have a test file called testPage with the following text:

|| '''Title1''' || '''Title2''' || '''Title3''' ||
|| Cell11 || Cell12 || Cell13 ||
|| Cell21 || Cell22 ||
|| Cell31 || Cell32 ||
|| Cell41 || Cell42 ||
|| CEll51 || Cell52 ||
|| Cell61 || Cell62 ||
|| Cell71 || Cell72 ||

That I want to look like:

{|
|'''Title1''' || '''Title2''' || '''Title3''' ||
|-
| Cell11 || Cell12 || Cell13 ||
|-
| Cell21 || Cell22 ||
|-
| Cell31 || Cell32 ||
|-
| Cell41 || Cell42 ||
|-
| CEll51 || Cell52 ||
|-
| Cell61 || Cell62 ||
|-
| Cell71 || Cell72
|}

I have a script:

#!/bin/bash

isTable=0
beginTable="^\|\|"
lineNum=1

while IFS= read -r line
do
    echo "lineNum: $lineNum, line: $line, isTable: $isTable"
    if [[ $line =~ $beginTable ]]
    then
        if [ "$isTable" -eq "0" ]
        then
            isTable=1
            sed -r $lineNum's_\|\|_\{\|\n\|_' -i testPage #Begin table
            echo "begin table"
        else
            sed -r $lineNum's_^\|\|_\|-\n\|_' -i testPage #Define row ##DOESN'T WORK##
            echo "start of row"
        fi
    else
        if [ "$isTable" -eq "1" ]
        then
            isTable=0
            sed -r $lineNum's_(.*)$_\1\n\|\}\n_' -i testPage #End table ##WEIRD RESULT##
            echo "end table"
        fi
    fi
((lineNum++))
done < testPage

That gives the result:

{|
| '''Title1''' || '''Title2''' || '''Title3''' ||
|-
| Cell11 || Cell12 || Cell13 ||
|-
| Cell21 || Cell22 ||
|-
| Cell31 || Cell32 ||
|| Cell41 || Cell42 ||
|}

|| CEll51 || Cell52 ||
|| Cell61 || Cell62 ||
|| Cell71 || Cell72 ||

I can't figure out why it stops substituting after three iterations even though the loop reports the appropriate line and line number as well as matching the appropriate logic.

Any help is appreciated.

For clarity, testPage is a portion of a larger file, so sed beginning and ending flags (i.e., doing different things on lines 1 and $) won't do for me.