GET_VAR does not resolve recursively on v12.x and v11.x. From v9 SP4 to v10 SP4, GET_VAR resolves recursively. This means, if a value contains an "&", the script processor tries to resolve this. This has been changed.
Static variable 'MYVAR', Key = 1 Value = 'Schmidt&Partners'
:set &partners = 'no'
:set &value# = get_var('MYVAR','1')
The variable &value# will contain therefore:
v9 SP4 to v10: Schmidtno
v11 : Schmidt&Partners
With v10 SP4 HF1 the behavior was configurable (key RESOLVE_GET_VAR in UC_SYSTEM_SETTINGS).
In v11 the configuration option was removed. As a conclusion all variable values, that should be resolved recursively, must use the Script function RESOLVE_VAR.