Multiproject:site-deploy copying files twice

After the Checkstyle run, seemingly as part of "building reactor projects", it copies some files for each subproject, which is unexpected to me. While this can seem trivial, the file copy time is half the build time:

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[snip]

[echo] Generating the Checkstyle...
checkstyle:init:

checkstyle:report:
checkstyle:run:
[echo] Using file:C:/devroot/healthmatch/Development/healthmatchmaven/../healthmatchbatch
/src/conf/checkstyle/checkstyle.xml for checkstyle ...
[echo] Now building reactor projects: [HealthMatch, HealthMatch Batch]
[copy] Copying 11550 files to C:\devroot\healthmatch\builds\healthmatchmultiproject\docs\multiproject\heal
thmatch
[copy] Copying 225 files to C:\devroot\healthmatch\builds\healthmatchmultiproject\docs\multiproject\heal
thmatchbatch
multiproject:projects-init:

multiproject:site-init:

[snip]
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Then, when everything is all done, the site:fsdeploy does the copy, as expected (and deleting all the previously copied files first!):

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[snip]

site:init:

site:local-deploy-init:
[echo]
site clean = true
siteDirectory = c:/devroot/healthmatch/sites/healthmatchmultiproject

site:fsdeploy:
[echo] Cleaning destination first
[delete] Deleting directory C:\devroot\healthmatch\sites\healthmatchmultiproject
[mkdir] Created dir: C:\devroot\healthmatch\sites\healthmatchmultiproject
[copy] Copying 15835 files to C:\devroot\healthmatch\sites\healthmatchmultiproject

BUILD SUCCESSFUL

[snip]
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In this build process, the file copy time takes a very long time with almost 16,000 files!