Breaking change from 1.8.10 to 2.0.3 for union types of class having functions

[0815fox]

TypeScript Version: 2.0.3
Transferring my project from 1.8.10 to 2.0.3 ran me into a bunch of issues all similar to the following simplified code example (test.ts):

class X<T> {
    bla(x:()=>T|Z<T>) {

    }
}

class Y<T> {
    bla(x:()=>T) {

    }
}

class Z<T> {

}


function doBla<T>(In:T) {
    const x:X<T>|Y<T>|T = new X();
    if ((<X<T>|Y<T>>x).bla) (<X<T>|Y<T>>x).bla(()=>{return In;}); //<= compiles in 1.8.10, but fails in 2.0.3
}

Expected behavior: compiles (as on tsc 1.8.10)

Actual behavior: does not compile on 2.0.3, see below

mk@mk-actifsource:~/tmp$ tsc -v
Version 1.8.10
mk@mk-actifsource:~/tmp$ tsc test.ts
mk@mk-actifsource:~/tmp$ node_modules/.bin/tsc -v
Version 2.0.3
mk@mk-actifsource:~/tmp$ node_modules/.bin/tsc test.ts 
src/test.ts(20,26): error TS2349: Cannot invoke an expression whose type lacks a call signature.

I tried to search for similar issues and found #7294, however I am not sure about relevance of that issue.

[ahejlsberg]

This is the same issue as #10025.

[0815fox]

However, #10025 states milestone 2.0.2 - this report is for 2.0.3. Is it really the same issue, which is not yet completely fixed, or just related?

[ahejlsberg]

It is the same issue, and it is unfortunately an actual breaking change. As mentioned in the comments for #10025, it happened to work in some cases (including yours) because of aggressive subtype reduction, but we need a different approach to actually fix the issue in the general case.

[0815fox]

For others finding this ticket: the currently open ticket handling that case seems to be #9104.
BUT: #9104 is itself market as DUPLICATE as well, however, I cannot find, which "not closed" ticket #9104 actually duplicates.
Can you give us a pointer, which open ticket handles the type inference issue?