Dear monermanush,
The problem of Juktakkhor/Yuktakkhara is not a problem of Avro or Unicode. This problem regardsto the font "Arial Unicode MS". This is a faulty font for Bangla. It cannot show Bangla properly, not only the Juktakkhor/Yuktakkhara but also the '-kar' as well. And unfortunately the different fonts of M$ Wind0w$ and M$ Office (which they claim as Unicode compatible fonts) shows different results. Only Vrinda, a unicode font from M$ family, can show Bangla 'almost' appropriately. If you ask for a suggestion the only option that we can recommend is use the free OpenSource fonts.
Lets see some results:
Test:1
Test Word: হিতৈষীM$ fonts:1. Vrinda:

2. Arial Unicode MS:

3. Lucida Unicode Sans:
Free Fonts:4. Siyum Rupali:

5. Solaimanlipi:

Test:2
Test Word: নভেম্বর M$ fonts: 1. Vrinda:

2. Arial Unicode MS:

3. Lucida Unicode Sans:
Free Fonts: 4. Siyum Rupali:

5. Solaimanlipi:

You can also check and download other Bangla fonts form:
http://www.omicronlab.com/bangla-fonts.html