The Wix bundle size was doubled after signing

Question

I'm trying to sign a wix3 bundle, following are my steps, the signed bundle.exe work perfectly, but size was doubled after whole process, any suggestion?

1. extract burn engine from bundle. the bundle.exe size is about 800MB, and engine.exe size is about 4MB.

insignia.exe -ib bundle.exe -o engine.exe
or 
wix burn detach bundle.exe -engine engine.exe

2. sign engine.exe. my organization use signserver solution, so my sign command like this. the signed engine.exe size became to 800MB，just like the bundle.

signclient.cmd signdocument ^
  -host xxx.xxx.com -port 443 -workerid 6 ^
  -infile ../in/engine.exe -outfile ../out/engine.exe ^
  -keystore ..\keys\xxx.p12 -keystorepwd xxx ^
  -truststore ../keys/codesign.jks -truststorepwd xxx ^
  -clientside -digestalgorithm SHA-256

3. attach the signed engine.exe back to bundle.exe, then got a 1600MB bundle.exe.
4. sign the bundle.exe.

Answer 1

I found the reason, my initial bundle.exe is not clean, my bundle.exe was signed one. if sign a engine.exe extract from signed bundle.exe, the engine.exe size will double after sign. but still don't know the logic inside.