anonymous function parsing bug?

Hi,

I hope this is the correct list for my question. I found a wired 
behaviour of my R installation on the evaluation of anonymous functions.

minimal working example

###
f<-function(x) {
    print( 2*x )
}(2)

class(f)

f(3)

f<-function(x) {
    print( 2*x )
}(4)(5)

f(6)
###

leads to

###

f<-function(x) {

+ print( 2*x )
+ }(2)

class(f)

[1] "function"

f(3)

[1] 6
Error in f(3) : attempt to apply non-function

f<-function(x) {

+ print( 2*x )
+ }(4)(5)

f(6)

[1] 12
Error in f(6) : attempt to apply non-function

###

is this a bug or desired behavior? Using parenthesis of coures solves 
the problem. However, I think the operator precedence could be the 
problem here. I looked at the "./src/main/gram.y" and I think that the 
line 385
    |    FUNCTION '(' formlist ')' cr expr_or_assign %prec LOW
should be of way higher precedence. But I cannot forsee the side 
effects of that (which could be horrible in that case).

If this is the desired behaviour and not a bug, I'm very interested in 
the rational behind that.

Best wishes,

Wilm

ps:

$ R --version
R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"