Unable to echo single character with zsh

Setup: OSX 10.11.5 El Capitan. Default (5.0.8) and/or brew installed zsh (5.2).

I have strange issues with zsh, where it seems to: a) mask single characters and b) adds strange control characters. This causes problems with pipes and parsing. It seems like zsh is adding extra or removing characters. It hasn't always done this, so I think it might be a configuration issue.

I'm assuming both issues are related and the first is easier to replicate.

If I set my shell to bash, then I can run the following:

Phils-MBP-7:~ phil-mac$ echo -n A
APhils-MBP-7:~ phil-mac$ 

Now, if I set my shell to zsh:

Phils-MBP-7:~ phil-mac$ chsh -s /bin/zsh
...
Phils-MBP-7% echo -n A
Phils-MBP-7% 
Phils-MBP-7% echo -n AA
AA%                                                                             Phils-MBP-7% 

Note how there is no single character version, and the AA version seems to have added a newline. Surely something to do with zsh trying and failing to make the output pretty.

Also, not sure if it's related, but in the terminal there is a small blue left square bracket that appears on the line above after pressing retu.

Any ideas? Thanks in advance.

Edits:

Result when running /bin/zsh directly:

Phils-MBP-7:~ phil-mac$ /bin/zsh
Phils-MBP-7% echo $PS1/$PROMPT
%m%# /%m%# 
Phils-MBP-7% echo -n A
Phils-MBP-7% 
Phils-MBP-7% 

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