I am using Workbench 18.104.22.1686 Build 410 and a Trados Multiterm 5 Termbase file.
Are you aware that this version is outdated? It was replaced by T6.5.2 (build 417) at the beginning of this year, and T6.5.5 (build 438/439) has just been released. Version 6.5.1 contained numerous bugs - this could be one of them.
As I cannot seem to locate this file using the newer Multiterm version, I have opened it in Multiterm 22.214.171.124.
You cannot open MT5.5 databases in MTiX, but there is a conversion utility called MultiTerm Convert; this is contained in MultiTerm 126.96.36.1997 (build 267), which was issued in the summer of 2003 and upgraded to build 279 in Februar 2004.
I believe all the settings are correct on Workbench with term recognition ticked and so on but when I open a translation section the multiterm gives the following message - "Source language was changed. The first entry is displayed."
In Options - Terminology Recognition Options, did you change the Terminology Provider to "MultiTerm 5"?
Best regards, Ralf