isAlways function is unable to prove a simple statement

I am using Symbolic Math Toolbox to simply see if below statement is positive or not:

(x - b - 2*c*d) * (y - b)

I am assuming that both (x - b - 2*c*d) and (y - b) are positive.

syms x y b c d

assume(x - b - 2*c*d > 0 & y - b > 0 );

After making these assumptions, I checked if 'isAlways' function considers the assumptions. I got below results:

>> isAlways((x - b - 2*c*d) > 0)

ans =

  logical

   1
   
>> isAlways((y - b) > 0)

ans =

  logical

   1

Getting above results, naturally, I expect to see (x - b - 2*c*d) * (y - b) is also positive. However, I get 'unable to prove' error. How can this be possible ? What can cause this ? Here is the result I get:

 >> isAlways((x - b - 2*c*d)*(y - b) > 0)
Warning: Unable to prove '0 < (b - y)*(b - x + 2*c*d)'. 
> In symengine
  In sym/isAlways (line 42) 

ans =

  logical

   0