This is a problem for all Tcl 8.6 versions and is one of the reasons, why tcl 8.5.* is still recommended for the OpenACS releases. The problem is actually fixed on github since 2012, but there was no new release of tdom since this time. We have the following options
a) wait for a release / stable version and recommend tcl 8.5
b) add the (trivial patch) to the build process
c) use the head version of tdom.
So far, we sticked to (a). Variant (c) is no good policy, since this makes installs not reproducible, since tdom is potentially the "catch of the day". I'll bring up the question in the tdom forum...
