why pair ends data's ecah pair's alignment statistic and the sum of them are different

I have a sample's data, using illumina 's Piar End sequencing technology.

RE19E2T40PA_L1_I040.pairPrimer_1.fastq   (Read1)
RE19E2T40PA_L1_I040.pairPrimer_2.fastq   (Read2)

I have aligned both Read1 and Read2 to hg19 using BWA, and generated three bam file.

RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read1.sorted.bam   (Read1's bam file,  generated via command :' bwa samse' )
RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read2.sorted.bam   (Read2's bam file,  generated via command :' bwa samse' )
RE19E2T40PA_L1_I040.pairPrimer_1.fastq.sorted.bam         (pair end bam file,  generated via command :' bwa sampe' )

Then I using picard to generate alignment statistics.

java -jar /usr/app/picard/picard-tools-1.77/CollectAlignmentSummaryMetrics.jar R=/home/share/hg19/ucsc.hg19.fasta I=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read1.sorted.bam O=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read1.sorted.bam.stat

java -jar /usr/app/picard/picard-tools-1.77/CollectAlignmentSummaryMetrics.jar R=/home/share/hg19/ucsc.hg19.fasta I=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read2.sorted.bam O=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read2.sorted.bam.stat

java -jar /usr/app/picard/picard-tools-1.77/CollectAlignmentSummaryMetrics.jar R=/home/share/hg19/ucsc.hg19.fasta I=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.sorted.bam O=RE19E2T40PA_L1_I040.pairPrimer_1.fastq.sorted.bam.stat

Look below! The results are contradictory:

Read1's alignment statistic ('RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read1.sorted.bam.stat')

CATEGORY    TOTAL_READS    PF_READS    PCT_PF_READS    PF_NOISE_READS    PF_READS_ALIGNED    PCT_PF_READS_ALIGNED
UNPAIRED    225020    225020    1    0    127242    56.55%

Read2's alignment statistic('RE19E2T40PA_L1_I040.pairPrimer_1.fastq.read2.sorted.bam.stat')

CATEGORY    TOTAL_READS    PF_READS    PCT_PF_READS    PF_NOISE_READS    PF_READS_ALIGNED    PCT_PF_READS_ALIGNED
UNPAIRED    225020    225020    1    0    44101    19.60%

Pair End's alignemnt statistic (RE19E2T40PA_L1_I040.pairPrimer_1.fastq.sorted.bam.stat)

CATEGORY    TOTAL_READS    PF_READS    PCT_PF_READS    PF_NOISE_READS    PF_READS_ALIGNED    PCT_PF_READS_ALIGNED
FIRST_OF_PAIR    225020    225020    1    0    129286    57.46%
SECOND_OF_PAIR    225020    225020    1    0    87054    38.69%
PAIR    450040    450040    1    0    216340    48.07%

Read1 have 127242(56.55%) reads aligned by standalone while 129286(57.46%) reads aligned by Pair Ends.

Read2 have 44101(19.60%) reads alingned by standalone while 87054(38.69%) reads aligned by Pair Ends <--- This is so different, why?