You can do this and use newstate to tell you what form you're in.
Lua Code:
'[noform]0;[form:1]1;[form:2]2;[form:3]3;[form:4]4'
The issue seems to be that the form condition is firing before GetShapeshiftForm() returns information about the new form.
Switching directly between forms wouldn't do anything with your example because [form:1/2/3/4] is still true, so the state doesn't change except when your character registers as being out of form in between shifts.
Macro conditions are only evaluated every 0.5 seconds or something, so you'll have ambiguous results.