Typing Burmese on Mac

[Pasha]

Hello
I switched to Mac (OS X 10.5.6) - and try to understand how the typing
issue works here, meanwhile unsuccessfully.
I have installed UniBurma input source, and downloaded some fonts.

Using Neo-Office, Myanmar 1 works almost fine and the same result is
obtained whether I am in "U.S. extended input source", or UniBurma.
However, with Myanmar 3 happens something incomprehensible for me:
Trying to type it when in "U.S. extended input source" gives no result
at all. After switching to UniBurma- pressing a key gives no result,
but sometimes after 10-15 keys pressed suddenly all the text typed
(and hidden till then) appears. Sometimes, the program switchs
automatically to Tahoma font, and then burmese letters appear fine -
but it's Tahoma and not Myanmar 3.

I have no idea what's going on. Any hints? Where the problem is? Neo
Office? Input source/font incompatibility? How do people, who use Mac,
type Burmese in Unicode font?

Thanks