Confirmed in the 1.8 branch, r20872.
Fixed in the development branch svn://svn.zabbix.com/branches/dev/ZBX-3993
thanks for the speedy fix 
described problem seems to be gone in dev branch rev 20874
(1) might be unrelated, but the following unexpected behaviour can be observed :
a) follow the same steps as to reproduce the original problem. notice that it works ok now.
b) override the macro on template2 (add macro with same name but different value).
c) reload proxy config cache. according to my understanding, this is supposed to retrieve all config without any caching involved (verifying the proxy data, at least changes in item config seem to be picked up as expected)
d) restart active agent. it should now have all the latest config.
e) observe old macro value still being written to the file
f) let it run for a while. after some time period correct macro value (from template2) will start to appear in the debug file
<sasha> caching of macros in a version 1.8 is perform each processes separately (not by a global configuration cache), and refresh it each 5 min. Therefore there is such problem. In a version 2.0 macros are cached by a configuration cache.
<richlv> does "by each process" here refer to individual daemon processes (like poller etc) ?
<asaveljevs> What is the other way to understand it?
<richlv> "server", "proxy"
<asaveljevs> Ah, then yes, in 1.8 macros are cached individually by each daemon process.
Fixed in version pre1.8.7, r20952