巨坑：使用官方案例，开启分布式事务，执行了两次远程调用

官方案例：springcloud-eureka-feign-mybatis-seata
问题：正常执行完，account服务的decrease方法执行了两次。导致最后的提交SQL，也执行了两次。
环境：
- jdk8
- Spring Cloud Hoxton.SR6
- Spring Boot 2.2.6
- seata 1.3.0

io.seata
seata-spring-boot-starter
1.3.0


com.alibaba.cloud
spring-cloud-starter-alibaba-seata
2.2.1.RELEASE


io.seata
seata-spring-boot-starter



[截图：](https://inmd.oss-cn-hangzhou.aliyuncs.com/ScreenShot_20200809002213.png)

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Start with the springcloud-eureka-feign-mybatis-seata official example and the account service's decrease method, using the listed JDK, Spring Cloud, Spring Boot, and Seata versions. Reproduce the transaction and trace why the remote call and final SQL execute twice; done means the cause is identified and the example performs each operation once.

Written by the indexing model from the issue text.